My best friend hangs out with my ex.
I'll try to keep this as brief as possible... there is a lot that went down prior to this, but basically, my ex girlfriend broke up with me not but two weeks ago, and while we dated, she seemed to be very eager to get to know my two best friends, one in particular. Well, she ended up breaking it off with me because I guess I got a little jealous that she constantly wanted to hang out with my best friends instead of me. Also, she claimed to only like me as a friend when we started and said it just never grew into anything more.
However, now I miss her to death (even though I shouldn't, because she wasn't very loyal and flirted a lot), and my best friend hangs out with her behind my back. He probably knows I know, but doesn't make a scene about it and I already told him once that it made me really uncomfortable that they became such good friends, but he just doesn't seem to care and says that he will continue to be friends with her and "I can't stop him." He says that he is just being courteous and doesn't want to blow her off just because I can't take the breakup.
I'm just worried that she dumped me for him secretly, and I have told him of my suspicions, yet still doesn't listen to me. He says he would never date her, but I know him all to well to just take his word for it... Am I right to be mad at both of them? Or am I just overreacting. I know if would be a different story had I broke up with her, but no, it was the other way around. I just feel replaced and like he doesn't give a rip about my feelings. What should I do?