My ex and I

My ex and I have dated for well over a year and then he ended things and then he ended up with my "best friend" they've been together for 6 months now but he cheats on her a lot with other girls (including myself a few times) and him and her are expecting. He recently told me today that he still has feelings for me and they never went away and I still have feelings for him also.. I really don't know what to do cause I don't wanna ruin my best friend and I friendship and I don't wanna ruin things with him..