I have been in a relationship for almost a year with my current boyfriend. He dated a girl before me for two years and broke up because she cheated on him. He has never really mentioned her much other than she cheated on him and he wanted nothing to do with her. I know she tried and tried to get him back. I just found out through a friend that after my boyfriend and his ex split he continued to hook up with her for sex for quite awhile. Some of the time probably around four or five months overlapped the time him and I were sleeping together but during that time him and I were not serious and were not exclusive although I had no idea he was sleeping with her. I also found out that him and his ex use to have threesomes all the time and after they split they would still get together and hook up with other couples either friends or people they found online. This really bothers me and I'm not sure why. Maybe I'm worried since he use to have threesomes and hook up with other couples with her he will find me boring since I am not into that sort of thing. I don't know if I should confront him and tell him I know he was still sleeping with his ex and having threesomes and foursomes long after they broke up. He has never mentioned to me ever that he has had threesomes in the past or that he use to hook up with other couples with his ex I am worried that he'll soon grow tired of our sexual relationship. I'm just really confused. His ex too still after years texts him and tries to get him to meet up with her. I guess I'm asking should I keep all this to myself or ask him about it?

No, his past is just that, his past, if he was sleeping with others when he was or had promised to be true to you, that is not the past.

Now you do need to discuss, not in confronting him with possible gossip ( that may or may not be true, you were not there) but as to what sexual things you or he will or won't do.
Since he may have an incorrect opinion, since you did say you were having causal sex with him ( sex with no committment)

Enjoy what you have now, and leave all the insecure paranoid stuff alone, please. You had your fun back then, and so did he, now have your fun together and don't worry about what happened.

But if you know you both had fun having sex always protect yourself, like a responsible adult.

Let his past go its his, and likewise yours is yours it's the Now that matters the Moment.

dont trouble trouble till trouble troubles you, is my motto on these issues.

Its over you can't change it so ignore it...

Ever thought perhaps he has more respect for you that's why he hasn't asked you to take part in any 3 somes...

Oh and don't listen to gossip, its almost always made up or added to so cannot be relied upon as factual.

Well, it seems as if he has done nothing wrong. It is usually the other way around; girls don't want to hear about their boyfriends ex. If I were you, I would stop all this paranoid thinking and enjoy the here and now with your boyfriend. Too many relationships break up because of this issue. Enjoy what you have and be thankful that you have a boyfriend who is not hung up on his ex.

Thanks for all of your advice guys. And I think the majority of you are right and that I need to let his past stay in the past. Thus far I have no reason to believe that he has done anything behind my back since we became serious all of the things that I am worried about occurred before we were in a serious relationship. I guess its just a little hard as a girl to know that he sexually enjoys things that I am not willingly to take part in and his ex was although he has never brought it up to me in the year that we have been together he has never once mentioned having another girl or couple join us... so until I get some other sign I'm going to hope that he is happy with our sex life the way it is :)

I'm with everyone else here, too. Why worry about it? It sounds like he's happy with just you to me. Maybe he went through an experimental phase. Either ways, sounds like there's nothing to worry about.