I'll try to make this as as possible

I have been with my bf for over 2.5 years. Throughout this time we have had issues relating to his ex (they were together 5 years). In the beginning he told me she was good in bed. They had a rocky relationship but the sex was amazing and that was what kept them going back to each other. Then she would pop up here and there and he would say she initiated the contact, etc. Then he would try to make me understand that they were childhood friends and its hard to let go of that. We agreed he would only have surface contact with her - how are the kids, Merry Christmas, etc.

I've always been uneasy about her. Given their history I just didn't trust it. Whenever I became suspicious it would turn out they were communicating. We would fight and it would seem like I was the one with the problem.

Note: I knew him as a friend for 6 years before we got together. I knew about how many women he dated and what not. I just thought he was a horny SINGLE guy.

Note: Since I knew about his "amazing" sex with her it created a strain on our sexual relationship that we've never really been able to get past. HE says because he was rough with her (he ikes rough sex) and doesn't want to treat me like just a sex thing he finds it hard. Strange, I know. He loses his erections and I'm just not into it. HE's 50 BTW

Fast forward to this past summer (July). I know its icky, but I was feeling uneasy about us so I checked his phone. OF course I found they had been talking. I asked him and he denied it. I told him I knew and we had a fight and we broke up. I ended up talking to the ex and she filled in all gaps I always wondered about. Turns out they talked quite a bit. They remained sexual with each other for at LEAST 3 months into his relationship with me. To the point he actually told her sex with me wasn't as good.

So turns out they had sex 3 months into our relationship, they talked a lot, suposedly ONE time they rolled around in bed (with clothes on hahaha) but it didn't go anywhere because she stopped it.

HE lied about it every time they spoke. He never told me he saw her, went to lunch with her, rolled around with her. I guess he even called and asked if she was getting it like she needed it.

That's not even it! He also likes young girls. He flirts with them and in the past (in his 40s) he's slept with girls in their 20s. This past summer he took one of the girls he had a fling with (3 years ago) out to lunch.

Why oh why have I decided to try to make things work?
We go to couples therapy together. He seems to be honest now. He claims he hit a low point and HIS therapist thinks he's a sex addict. Thing is early in our relationship we went to couples therapy about her. He lied through his teeth. I feel the difference now - that he's being honest NOW. Even our therapist told me most people would leave.

I can give more details if you want them