My BF (40M) has slept with quite a few of his female friends, and their continued closeness makes me feel uneasy... how to proceed??

You asked for another option besides breaking up. Your only other option is to suck it up if you don't want to walk away from this relationship.

He is 40 years old, looks like he has been living like a bachelor for the past 15 years. Has a bunch of Friends With Benefits he didn't tell you about, somewhat understandably, he probably doesn't want to make you feel insecure but there is really nothing you can do besides break up and be with someone who is compatible with you when it comes to morals.

Unfortunately you don't get to ask him to stop being friends with these people, because of his age and the way he built his life to be, and it's very unlikely he would anyways. If you want to stay with him, do your best to rebuild the trust if it's possible. Of course you can always tell him how you feel, but will he be okay with all this snooping and demands or will he think you are childish and break up himself?! If you don't want the relationship to end, then suck it up.

/r/relationships Thread