Recently single from a LTR, my ex had a threesome with one of my mates and a guy she knows I don't like. Since then she's been spending a lot of time with people she knows I dont like and that I openly have a problem with and it's been really getting to me. I've slept with other girls since her and she never really meant that much to me but she has really got into my head with this situation. We have seen each other in bars and clubs and I have just left instantly cause I can't bare to look at her.

How do I deal with this problem and what should be my plan of action?