my bf has been cheating on me for 2 years.

(Sorry about the long post)About two years ago, he confessed to me that while I was abroad taking care of my dying mother for couple of months, that he met this guy and they jerked off together.It was the worst time of my life because I was grieving my mother's loss and at the same time felt betrayed by the second most important person in my life.After long talks, I decided to forgive him as he used the excuse that he felt lonely and alone and he went along with what the guy wanted because he liked the attention.He then asked for an open relationship, something that I never imagined I would ever agree to be in. I went along with it because I love him and I probably have no self respect.For months, nothing happened, neither of us met anyone and he didn't show interest in meeting anybody. Although he is gorgeous, he has a lot of self confidence issues and so that plays a role as to why he doesn't meet anyone.Then few months ago, after months of us not being happy with each other, we broke up (for the first time). He broke up with me to be more specific, saying he is not happy. I didn't stop him.We were broken up for about 3 weeks. I met few guys on successful dates and then eventually he wanted to get back with me saying he loves me and all of that. So hesitantly, I agreed. Figured that he saw the outside world and realized how much I mean to him. He also said that he doesn't want an open relationship this time. That he only wants me and thats it.Couple weeks ago, I complained about me not being happy sexually with him, we rarely do anything and if anything happens, it's always me pleasuring him and thats all. He apologized and made up couple excuses and said he'd work on it. The next day I went through his phone and I discovered that he's been talking to guys on this fetish website (which we are both on and I allowed both of us to be on it in the goal of making friends with people with the same kind of fetish) not only he's been talking to these guys sexually, but he admitted to me that he's often jerked off because of these conversations which would explain the lack of sexual interest he has.He again apologized and made me feel sorry for him and promised he'd not do it again.Then last night, I go through his phone randomly to find that he's had the guy he cheated on me with on snapchat, registered under a different name (one of his old friends) and it shows that they've been in contact often. When I questioned him about it, he admitted they've been messaging occasionally and even having sexual conversations and that he's even sent dick pics to him.I feel like my entire world is just a lie. I don't have enough self respect or self confidence to walk out. He says now again that he wants an open relationship, that he is not happy and that he's just been trying to please me and make me happy, which I called bullshit on because he's literally been lying and cheating behind my back for 2 years non stop. He never tried.I'm not really looking for advice, only because I know what the 'right' thing to do. I know I should walk out and leave him. I'm a good person and a good boyfriend and I know I deserve better... I just wanted to vent because I can't share this with any of my friends because I'd feel ashamed.