When the victim becomes the monster

This has started back many years ago, I had just gotten out of the Navy and gotten back together with my high school sweet heart. Things were going great reconnecting after losing her while I was over seas, we would talk on the phone or send letters. This was before everyone had a cell phone so we would do what we could to stay connected, we lived in different states now but wanted to make it work and would take turns driving to see each other as often as possible. A little while into the relationship she tells me that she needs to go out of state and pick up some things left behind at her former boy friends house, which included a pet. Not thinking anything of it I wished her well and told her I would talk to her when she got back. Few days went by a bit longer than I had originally expected but nothing crazy and I got a call. She was different more set back and distant from me, I couldn't figure out why but I kept asking her if everything was alright. Soon after she came out with it she had said that the feelings her and her ex boy friend had where rekindled and things happened while she was down there. I asked her simply is that what she want or does she want to continue to be together? She told me she did not know, at which time I told her goodbye leaving that part of my life behind me.
During the end I worked with what would later turn into my wife. She had just broken up with her boyfriend and was trying to give me her perspective on what my now ex girlfriend was doing. Before long we started dating and things where great putting that painful part of my life behind me and trying to move on with this new girl. Things were going well again went through the honeymoon stage and as things settled down like many couples we started having little disagreements. Nothing major that I would have ever thought was relationship ending by any means, but one day she came to me and said I think we should take a time out from each other for a couple of days. I was a little confused but if thats what she wanted than I wasn't going to argue the point. The next day I get a call and she wants to come over to talk, figuring that this was part of the piece of talking through whatever issue she had I agreed. When she got there she broke down in tears and told me she left me that day and went out that night with her co workers and wound up sleeping with one of them. she felt guilty and sorry and wanted to be together still she was just being selfish. It really hurt at the time but I agreed to not give up on us and work it out. We were working on us for a week or two and she started getting distant again, within a day or two she again comes to me sobbing and sorry she had slept with the same guy again. I was now devastated wondering what I did wrong. She again begged to let this work out and that she would completely write him off, which she did attempt but he got jaded and started sending inappropriate items to her work with her name on it embarrassing her, which became the new focus and the pain of the situation was put aside to handle that situation. That was it for awhile but the damage was done, I became accused of every girl I was friends with as being someone who I was or they were interested in doing more. Before long it was fight after fight of who I was with and what I was doing. Our neighbor who was very flirty and definitely to free with her sexuality was a constant argument as we struggled now through the relationship until finally we broke up due to the constant arguing and non communication.
9 months go by and we start talking again and things start to reignite feelings between us again to the point where we started seeing each other on a consistent basis, not straight out committing to being together but definitely not being apart. One day we have a discussion and she just wants to get away and be together, so I arrange a weekend to the shore and set the reservations pay for it all and we go. Her only request is that we bring along her little niece because she has never gone before. I thought ok this could be a good bonding time for the family as well so yeah we can do this. While there she seemed very hesitant to be affectionate which at first I thought was due her niece being around. As the days went on she spent time on her phone while I watched her niece by myself which I thought was a bit odd and rude but let that go as well. Over all we had a nice time and wasn't worth the argument. Days started to go by and more and more little things started to happen that just didn't fit right. Timelines just slightly out of place, movies she doesn't rent left on the table, a growing distance in how she acted. One day she tells me she isn't feeling well and is going to call it a early night that she would talk to me tomorrow. I told her to feel better and left her alone that night, and in the morning I text and called to check up on her to make sure she was alright. With no reply to multiple attempts I reached out to her mother and told her the situation. She also attempted to get in contact with her, now worried I drive over there only to find that she left the bathroom window open and the sounds coming out of it were earth shattering that will not leave my mind to this day. I banged on the door and confronted her with what I knew was going on, angry and hurt. Days go by and she begs and pleads with me to again make it work she is done with him she picks me. So again I try to make it work and through a lot of rough days we push through trying to put the nightmare behind me. As she actually found ways of turning all of this into not being her fault and focused on everything I did wrong and unfair stipulations I put on her because I wanted the guy she cheated on me with out of her life. Down the road we finally got married and had two children things were rough from time to time but that all seemed to be behind us. Then my youngest daughters 2 year birthday party we invited family and friends she invited some people from work, introduced me to them all and had a nice day not thinking anything of it. A few weeks later she got a new phone asked me to transfer pictures from the old to the new one and I find some very suggestive pictures of her in not much. I confronted her with them and she starts by saying that they were for me, she just never got to send them to me. I reluctantly believed her for lack of having any evidence to say otherwise, until a few days later she sits me down and tells me that she was actually sending them to the same guy I had shaken hands with at my daughters birthday party weeks prior. She swore up and down that nothing else happened but that she had to tell me because his wife found out and is crazy so before she told you things that weren't true she wanted to tell me first and I should not talk to the wife if she calls or texts. Stupid me I believed that although I knew something wasn't right about it.
More time goes by and we become distant with each other I start to let my attention move to a online video game and she spends more time out or being apart. Any intimacy between us had to be started by me and it became excuse after excuse on why she wasn't ok with it. Always being my fault on how she was made to feel, we tried couples therapy but she rejected the therapists suggestions, never wanting to go back to it again.
Till finally something broke in me or was breaking the whole time, and I found a female friend online that we started to connect as she was going through a very similar situation, in fact jokingly celebrated each of our 1 year anniversary for not being intimate with our partners. Which turned into a online fling for a few months before it was discovered by my wife who was pissed beyond belief. I had felt guilty not really wanting that but feeling like what I did have was lost. It hit me hard and I ended all contact with the girl online and focused on us and trying to put the pieces of the marriage back together. for the following year again it was rough she was so set back and continually throwing what I did in my face as to why she doesn't know if we can work through it. Until finally I gave up and we separated, which quickly brought to light that the same guy she had sent pictures to a few years back was now back in the picture and she was contemplating going to be with him but as I left she realized again that she wanted to be with me. For me the damage was done and so I left and we got divorced.
The next chapter in my life was shorter and during the separation and the end I met a girl who I liked and we started seeing each other for about a year before things started again to get a little weird she got distant and there were rumors of a guy she was hanging out with. She became more worried about what i was doing and who I was with. We had a big fight and it was over and she was out of my life for what I thought was good. she wanted nothing to do with me, and so we went our separate ways.
A few months later I started talking to someone I used to know from work, She was married looking to get divorced. I was going through the end of mine and we had a lot in common we connected on so many levels immediately. To the point I actually started believing in soul mates and everything was perfect and when I say perfect like that couple other people look at and go omg how can they be so perfect like that almost disgusting lol. We had one issue that arose with my ex girlfriend, they knew each other from work and when we first started talking I found out how much she disliked the place I kept that I had dated her. As things got really serious with my new girlfriend I didnt want that to be a bigger issue so I confessed I did date my ex. This put a small wedge between us as she is a no lies person even if I came clean or it was a small one. little did I know at the time what I had really become. Things were great time went on months felt like a fantasy, then out of the blue one day my ex gets ahold of me and needs to talk its important. reluctantly I agreed to hear what she had to say she actually tracks me down and has me pull into a rest stop off the highway where she proceeds to tell me that she is over 6 months pregnant and she just found out. My whole world just fell out from under me as I had written her off and accepted to never speak to her again and now I am forced into a choice of being in the babies life or not and on top of that she wants to make it a family and she was so sorry for all the things she did and said. I told my new girlfriend and yet another wedge was thrown into our paradise. Few weeks go on and her husband who was removed from the house the charges were dropped and he comes waltzing in again and wants to repair the marriage. My girlfriend now wants to not destroy the family and wants the kids to have a normal family if possible so she agrees to work on things with him while discussing with me that she would understand if I left but she wanted to be with me and doesn't think his new ways will last. I agree to wait for her as she sorted through her mess, until one day she comes to me in tears as he has been asking for sex from her since he got there and that night she felt she needed to comply with him in order to make him feel like she was trying as well. Devastating I did my best to understand the situation telling her you did what you had to do to make it work I still loved her and would be there if it doesn't work. His birthday rolled around and she took him out to celebrate, not liking the situation myself but respecting it they went out and did things we had planned before he came back which in itself was painful, but then after I had to go through a we had sex again and my ex girlfriend comes back into the scene with check out these pictures of them together at the event that I could see on Face book cause they were blocked from me.
I became a monster after that I wound up sleeping with my ex girlfriend while she was with her husband then felt guilty and lied to her about it and everything around it. I sought attention from any and every girl I could flirting and text inappropriately at the first sign of un easiness in the relationship. I devastated my girlfriend as the lies and flirting went on for years ending in getting her family and our friends to take my side of the story even with the twisted lies. I don't know why I became the very thing that crushed me over the years. Or why I did it to the one person I truly loved more than all of them combined. If someone can please help me understand myself I need help because I don't want to be this monster I have become. I just don't know how to stop it.