What should i do ?

I'm currently talking to this guy , who is so called my ex-boyfriend, we been working things out for over a year now and i feel like he doesn't appreciate me . i tried leaving him but he would always find a way to get back to me , i love him , but i can't anymore . when he does try to contact me part of me starts hoping he'll changed but he doesn't . Fast forward, i now fantasize about his best friend and vice versa but i'm scared . his best friend had s** w mine also . what should i do ? i honestly don't care about neither , they already did me dirty , but it's not about revenge. it's just the urge .