Am I making a BIG mistake by being in an open relationship?

Me and my boyfriend have been together for 5 months now. I am an athletic 24 yr old, and my boyfriend is also athletic, he is 29. Our sex life has been pretty good. We would have sex about three times a week, sometimes four times a week or sometimes just two depending on how we felt,(but he is addicted to oral sex so he gets alot of that during the week) since we are gym rats ( but going to the gym and the supplements he takes does affect his libido sometimes). Recently, he had begun to be distant, cold, and wouldn't talk to me. I asked him if he would like to talk about it, and he told me no, he just needed space. I asked if he wanted to break up, and he said no, but he would not give me a reason for wanting space. I said ok, and tried to give it to him, but I developed serious anxiety because he would not tell me anything just that he "didnt know what he wanted right now". He told me that it had nothing to do with me, and that I am "too good for him, I am perfect in every way" and that it was him with the problem, and that he needed to focus on himself. I told him take some time. The anxiety continued to push me to extreme levels of misfortune. I then texed him and told him I needed to see him. He told me it was ok to come over, so I did. I wrote a letter to him the day before to be clear about my feelings toward him. I told him that I refuse to give him space without a reason, and that after all the effort and time Im trying to put into the relationship, he at least owed me that. I also told him that I wouldnt give up on him so easily. He looked at me like a sad child, with tears in his eyes and told me that he was tired of hurting women. He told me that if he told me the truth, I would leave him and that he didnt blame me if I did. I told him to be honest. He then told me that he loves me, and wants to push me away because he doesnt want to hurt me. I told him i wouldnt leave his side, and to be honest. He tells me that he loves sex and thinks about having sex with multiple women, and he cant help it. He tells me he is a nympho and masterbates all the time. He says he wants to have sex with a girl and have me watch, and that if he cheated he wouldnt care or try to hide it from me if I found out but prefers that I dont know about it. He told me that he is being honest that he hasnt had sex with anyone else yet but is afraid that if he is left alone he will. He told me he most likely will act upon these impulses, and he cant control them. I even picked up his phone and found out he was talking to another girl. He told me he was, that he is sick, and has a problem. But he told me he hasnt had sex with anyone else, but most likely will. But made it clear that it was just sex he wanted from other women, not a emotional connection like he had with me. He told me thats why he wanted to push me away. He wanted to save me from his "sick sexual mind". He tells me that he doesnt want me with anyone else, but doesnt want to hurt me or hold me back from being happy. He told me that it is a game to him honestly and that even I was when we started seeing eachother, but then he developed feelings. I also want to point out that my boyfriend was adopted at the age of 6 or 7, he had problems with drugs as a young adult, and he is currently in and has been since we met a rehab program which he is doing so well, I am so proud that he has been sober for a year. He told me he wanted me to stay and that he understood that he was being selfish. The first thing I told him was that I understand and thanked him for being honest. I also told him that I also have issues with sex. I am also a chronic masturbater and I also have rape fantasies and want to have a threesome. I also revealed the truth about me being bi sexual. I told him that I was willing to try to have an open relationship, but that I want to be and will be the priority over any girl. He told me that he only wanted me emotionally, it was just about the sex with other women.
I told him that I will come first, no mattar what. I also told him that he has to make time for me. We agreed that weekends would be our time together and that occasionally meet during the week for sex or to see eachother. He told me he doesnt want me with other guys, but I was welcome to be with girls if I wanted. I agreed. I told him that I want him to call me or text me when he gets these urges and try not to commit them, but he told me that it wont be easy and he will slip which is understandable, because it is an addiction, I cant blame him. I also laid down the rule that with other girls he will use protection. Together we do not. He is clean and so am I, I also take birth control. I made it clear that eventually I would like to settle down and dont want this lifestyle for long and he said he will work on it, because he wants this relationship and wants to also settle down eventually. Another important point that I should make is that my boyfriend had been my first kiss and been my first intimate relationship (yes he took my virginity) The problem is that we both have issues with sex, but we are very both jealous, and dont want to know about whom the other is involved with. I am starting to feel confused and stupid. Am I making an enormous mistake? I dont want him with other girls whatsoever, but I said that I was willing to try, and I am. I just feel like this is dangerous and not right for either of us. I also love him very much, and dont want to end things. I know only the answer lies with me but I feel like some insight might be helpful for me to understand and be straight with my feelings. Am I being a fool because this is my first relationship? Is he just using me? Im unsure now, and left at a crossroads. Im thinking that I will stick with him, but eventually if I find an amazing man that wants to commit to me and only me, I will have to drop him and move on, but then when I think like this, I get upset because I want to stay with him. My heads telling me RUN, but my hearts telling me stay. Am I fooling myself? Please can someone help, and give insight. I would like to hear a point of view from someone who suffers with this addiction. Is it possible for him to be faithful?, it would be very helpful.