Do I have my head on straight on this?

So this might get a lil longer sorry, maybe I just have to write this off my heart...
(sorry for my primitive language too, but English is not my first language)

One day in a chat this young girl writes me. She is 18 and lives 30 minutes away, I'm 30 by the way.
Immediately I suspect her being a fake profile as so many before. So I answer rough as it is the best way to get rid of those people. But she keeps writing me even thou I'm not really that nice. Yet she does not ask the same stupid questions like all those other women. So I'm kinda interested and we end up writing for about a week. Actually it is really fun writing with her but as it is going deeper and deeper I'm blocking again. I don't like to give away personal information online to some stranger without a face, who knows whom I'm talking to. So I tell her I'm not going deeper into things if we have not met in reality, thinking that will finally take her interest as most fakes don't tend to meet you.
But she agrees!
I'm not even sure why I actually went there. She was there, she was beautiful, she was kind, yes she was 12 years younger than me but her thoughts were mature.
As there has been a sexual tension in our chats and I was still unsure if this is some kind of joke I did not expect much. That is way I agreed that we watch a movie at my place, I knew where this would probably go. And it did, we had sex. Not the best of course but the best sex I had till then.
So it was just a one night stand, I was just that older seasoned guy she can have sexual experience with? I did not care, I did not expect much anyhow.
But she called me back and we kept on talking. At first she was just curious having sex with an "older" experienced guy like me. She admitted the thought turned her on. But after our chats and especially after she met me she started to like me beyond that. I admitted that I thought she is a fake and all is just hoax. And that I slept with her because of her youth and I was sure it is going to be a ONS anyway.
From this moment we started talking open about everything.
She hoped we stay in touch and maybe have little affair as she was going to move to another city in about 6 months anyway. She did not want to have a real relationship because of this. Under these circumstances I agreed thinking what can be bad about some causal sex.
I told her what kind of relationship I'm looking for. I don't want anything solid. I don't want to say that we are "together". Especially cause I don't like the rules and all that comes with it for most of the people. This doesn't mean I'm into an open relationship. But I think if anything is forbidden one will do it anyway and then he/she will try to hide it. So if something happens this is okay as long as we tell each other. So the other one can decide for himself if he/she wants to go on then. Being honest and sincere is the most important thing for me. Everything is open and "allowed". In my opinion regarding to what someone sees in another one he/she will react in an appropriate way. If someone really likes me as she claims she will think twice about sleeping with someone else as she must know that it could ruin our relationship. But at the end I want to decide for myself if I can go on like this, I don't want anyone to take that decision for me.
She had to think about this for quite some time as it was difficult to understand for her. And I made her think about it for a week. She wanted to just "be together", have a boyfriend. But eventually she agreed she is okay with it.
So we met several times. But we did not have sex solely. Her company was nice and we went to the cinema, museums and other things. It went well for some weeks until she stayed at my place over the night. We could only stay at my place as she still lived with her foster parents. He real parents are divorced, her mother has some serious mental issues and hit her in the past. Also she has a bad relationship to her father, who seems to deny her. He favors her little sister and almost ignores her and her feelings. So they have not spoken to each other in several years. Which must have been difficult for her especially because she would have needed that support when she had to live in foster homes and so on. I bet those are not the nicest places, who knows what happened there, and knowing there is a dad you could go to if he just accepted you must be terrible.
So as she stayed at my place I overheard her on the phone with her foster mom. She lied to her about staying with a female friend for the night. I confronted her with it and she confessed she was afraid telling cause she thinks her foster parents would not allow it. I did not know what to think of it but I was young too, wasn't I? I could understand that it is her first real "relationship" and I'm much older than her. So I said its okay but I'm not going to lie for her and this will be something that is between us unless she tells her parents. She said she will do if she feels it. In fact it took quite some time to tell them, see below, and it made me question if she can lie to me as easy as she does with her foster parents. She has some quite solid relationship with them and they got really close. So there was no point in lying to them, yet she did.
There was another incident a few weeks later. We were at my place again, she was browsing facebook while I was cooking for us. I could see a chat message from a guy popping up and she was answering. So I was a bit curious but as I approached she quickly hid the window. I confronted her again, she said she felt really sorry but she thought I would take it the wrong way. With all the lying in the background I felt a bit unsure about it. But at that time I thought that she would be gone in a few months anyway and it was probably mainly sex too.
Those were the only two things for a while. Other than that it was great especially when we were together.
Things got more and more intense and she told she developed strong affection for me. I was sure she fell in love. Knowing she would have to move I would have never admitted any feelings like this.
Then she had to go to the town she was going to move to for two weeks. She did not know anyone there or anything to do so she got bored pretty fast. Therefore she went to a bar one night the first weekend and met a guy straightaway.
I was shocked because I surely developed emotion for her too. But I have to admit I have to give her credit for telling me at all. Yet she did not hesitate to add that he was "pretty hot" and I have no idea to day why this would have been necessary. Also she would met him again.
I felt betrayed and used somehow. We were not in a relationship but what does it say if just one week away she has another guy? God knows what she did with him? I mean I know she could be pretty straightforward, not? And she could have done anything, how would I ever find out?
That she seemed to have forgotten me after only a week hurt me so much actually. I broke up with her when she came back. She was pretty down and claimed nothing happened with the guy. She had not understood what kind of relationship we had and I wanted. Still I felt I got stabbed through the heart and thought it was a good decision. I thought it must have been clear that there is more between us and such a thing would get between us. Especially for the way she told me. Telling me that he is pretty hot when I am away for hundred miles, not being able to do anything about it. It felt she did it on purpose. Did she try to get me jealous? Did she want to provoke me? Some female friend even suggested she made that up to get me out of the corner, to make me admit I love her (too).
There was no contact between us for almost a month when she suddenly contacted me again. She was not able to stop thinking about me. Again she apologized for what she did not knowing that her doing hurt me so much.
As I could not stop thinking about her either and I was not sure if I made my point clear enough about how I think that relationship between us should be I agreed to meet again. We started to meet again regularly just where we stopped before. She told her foster parents also. Although that went not well later as I found out she had not told all the truth that she was lying to them. Because the foster parents wanted me to meet with her son to check me out which I thought is a stupid idea. I would have met with them if the situation allowed it, but like that? But I can understand it obviously she did not tell them much so they could understand the situation. Yet later she claimed to have told them all the truth.
Anyway it still went great then until she had to move to the other town far away. She made plans to see me on a monthly basis. She would get a job so she could afford the flight tickets.
I brought her off that idea and told her it will not work out. She will be far away, new school, she will meet other guys, maybe the one from the bar. Soon she will forget about me and it will probably be better. I said we could stay in contact but I'm not going for a long distance relationship. There was a lot of crying involved but I guess eventually she accepted it. She said she has deep feelings for me although she did not admit to be in love. And I would not have said anything in that direction for sure as it would only give her a false impression. There was no chance we could be together for at least two years. And that is a pretty long time.
We kept in contact, in fact we wrote every day via whatsapp. It must have been thousands of messages each day.
She wanted to fly back the next month but I brought her off that idea again. I blocked her and told her she should get comfortable the next months. We could see us again in a few months. She visited me two months later for almost two weeks. It was intense. We hadn't been that much together in all the time. Although she went to her friends and real family often. But she slept at my place almost all nights.
Then she had to go back again. We kept messaging a lot and it was good so far.
But jealousy started to emerge even more, especially on her side, she was ridiculously jealous. If it was for her I shouldn't go anywhere as I might meet a woman there. I thought this is a bit strange as I never gave her any reason to think that I would actively search for another woman. Other than the open relationship thing. I mean it was her that met a guy in a bar just after one week. I only told her that I'm not going for a solid relationship with her. If it happens that I meet another girl, I'm not going to step back because of her. But as we agreed to be open with each other always I would immediately tell her anything that happens. So she could always react to it. If she can't have contact me anymore because of whatever relation I have to another girl I am fine with her breaking up any contact. At least that was what I hoped she would do too. But it was not like I'm jumping on other women now she is gone.
We held contact until Christmas. Only once there was another strange coincidence. We were chatting on the chat we had met. She talked to me but suddenly her answers took some time. So I wondered what she is doing as it started to get a bit on my nerves waiting for the answers. I especially took time for her as she wanted to talk to me that night and now she seemed to do something else. So I asked her, she admitted that she wrote with another guy too. She had no intentions with him although he lived in the same town she lives now. She told it was funny how much effort this guy put in writing to her. He wanted to have sex with her but she denied it. But she told he still keeps trying and she liked it how she could reject him and kept on writing with him and doing so.
I told her if she thinks it is fair to stall him like that and if she wanted to be treated like this. She agreed and claims to have broken up contact with him since then.
Yet it happened several times that she came onto me wanting to chat and then not giving me all her attention. Her answers took time or she suddenly went offline on very short notice. I felt that she did not put enough thought into my position that I had to take time to chat with her. I felt a bit used again, as being just that guy who is there when she needs him. And obviously I was wondering if she might chat with other guys when this happens.
We had quite a few arguments over this and the jealousy topic also.
New Years Eve she visited me and it was wonderful again. Actually it was always like this. When just chatting we had our problems and when we met in reality everything was forgotten. We said several times we need to talk about everything. But we never had the guts as we just wanted to enjoy the time together.
When she left to fly back home it was a lot crying involved again. She flew back in the evening and had to take the train home from the airport at night.
So naturally I liked to hear from her after she made it home. To see she is all okay. But nothing, not a little message. The next day she told me she had an intense talk with her foster parents right after she came home. But still I thought that a little message had taken no time. Wouldn't she know that I bother a bit that she is alright?
It got me thinking again.
Does she really care about me as she claims? Am I just the guy that is "there"? Does she just pretend to be jealous? Why is she so different in reality than in chat?
So contact ceased much. Two weeks later a friend from the old town visited her. They wanted to go to a party together so she bought a new dress for that.
She send me a photo over whatsapp and all I could think is: WTF!
This dress was nothing but slutty. It had a sheer v-shaped cleavage so you could see all her breast through it. Actually they were pressed together by the dress so they came out even bigger.
She must have known I would be jealous because of that dress, I would not like it and feel bad if she goes to a party like this.
Still she sends me that picture of it asking me if "that is okay and I like it".
Obviously I told her what I thought of the dress. She bought it anyway and we had quite some argument over it.
Why else do you go to parties other than flirting with people? It is THE hook-up spot to go to.
I can manage that she wants to go to a party with her friend just for fun. I'm not that jealous, but with a dress like that? What should I make out of this?
After the party she claimed that "believe it or not" no one talked to her. But later she admitted that actually two guys contacted her. Yet she claimed she had told me, which is just not true.
She told me that one was coming up to her and she rejected him right away. But another guy kept trying to talk to her. She claimed she had no intension, just answered him and told she liked it how he tried to get in contact with her and how she could reject him.
I felt remembered to that guy from the chat.
It seemed she likes to have the power over men approaching her and I questioned if I'm not one of those men.
Also pinching the picture of that dress felt like pinching that the guy from that bar was "pretty hot" in my face.
Why does she do it? Does she want to get me jealous? Is it some kind of game? Is she angry at men and is this some form of payback? Is it because of her bad relationship with her father?
I felt like I could not go on like this and told her I need time to think about it.
She obviously felt something is quite wrong as she claimed she always feared I would break up with her when I'm taking some time to think about things. And told me that she would not want this to happen as she is in love with me. It was nice to hear although I knew it anyway for some time. But it also felt a bit like a way to keep me with her.
Before I could come to a decision she managed to hit another one. We had open talks about everything especially sex. So we talked about our unfulfilled sexual fantasies some day. I never had a threesome and what guy does not want to have one? So I told her this is currently the only fantasy left.
So she knew that carer of her sister that had moved to the same town only a few months before she did. They met several times and got well with each other although the carer is 30 just like me. She actually told me she had sexual thoughts about that woman. Like a foursome with the boyfriend of the carer. Although she still was not into women, more like swapping or something. I was puzzled.
But what really nailed it was the fact that she told that carer, she only met a few times, that I want to have a threesome.
I thought this was a huge betrayal of trust as it must have been pretty darn clear that it is not okay to talk about this to other people especially strangers. We have had talks about such things and I made my point clear that I'm not okay with her talking about our sex life to her friends.
So I had no idea how she could think it would be fine to tell an almost unfamiliar woman these delicate and private things about me.
I took a few days but I knew immediately that this is the end of it.
So I broke up with her again, telling her that there is no third chance. This was almost one year after we initially met. We already had made plans to go on vacation in the summer and probably more. And she claimed she would look forward to the things that would come.
She could contact me via mail as I know how it is to have open questions left but I would not accept mails like "please forgive me" or anything.
She did not take this offer thou to this day.
But she kept stalking me. Looking at my profiles online. So I banned her on everything, facebook, that chat, whatsapp...
It works for everything but the chat, she just made another nick and seems to keep looking when I'm online.
Early this month I had to write her as I remembered that I still need to send her some pictures I made of her and her sister. So I wrote her, she thanked me, everything seemed "normal". Still few days later she writes me again she has some problems with her laptop which I installed.
Problem is although I initially wrote her I think she tries to stay in contact now.
And even bigger problem is that I actually wish that this is the case.
I can not get stop thinking about her. I can hardly think of the bad things just how good it worked despite those few things. And somehow I might have contacted her for those pictures by purpose. Yet I know I had reasons for breaking up.

I'm not sure why I wrote this here. Maybe its because I'm a bit too confused by my own feelings.
Do you think I overreacted on her? What would you do or would have done in my situation?
Any advice on the whole thing?
I'd be glad about any thoughts about this! You can be plain with me I'm not week build