How to move on when your best friend is good friends with your ex.?

My ex and I were together for a while. we lived together for over 9 months. My best friend is still good friends with him, and i don't know how to accept the fact she still talks to him and sees him. We were gonna have a baby in Jan. but I lost it. He is still my whole world, despite everything he has said to me. I just don't know what to do.How to move on when your best friend is good friends with your ex.?
act like you don't care. be friends with him too! show him what he's lost. do things that get your mind off him. go to the gym and work out. look your best, eat healthy, and maybe get a doggie and stuff:) go out and hang out with friends and drink or out for lunches and dinner:) make your life fun and show him what he's lost and your better off without him, be strong!!!