The coment of Nicole the one before this coment is pretty much what you should do. And if he really liked you and really felt something for you i dont think he would be seeing someone else. Just tell him how you feel and explain to your best friend that you like her ex and if he feels the same tell her that you might go out with him or do something with him. But if he is seeing someone else don't do any sexual things with him, let him do it with the other girl he is seeing only if it true that he is seeing someone else.But don't feel bumbed out if incase he pretty much is seeing someone else and wants to be with her. Just try to move on and forget about him little by little. There's alot of other guys out there. Good luck with everything.

I'm just adding on to my coment i just had something else to tell you. Pretty much if u dont feel like doing sexual things then you dont have to. If your still a virgin then try not to lost it too yung. You might want to loose it with someone really special but this is what i think you dont have to take my advice for granted. And your best friend should understand what you feel and stuff she might not like it but i guess she will hav to know that you might be with her ex. The truth hurts. Good luck