Id like some help please

I had sex with a guy and we started to see each other casually, and I haven't felt this way about anyone since I lost my virginity. But his best friend, who is a work mate and also my best friends boyfriend has this weird obsession with me (he keeps telling me how'd he would be better for me than every person I ever date) and tried his best to keep us apart. His newest ploy is to have convinced this guy and his ex to try and work things out and get back together. They have been split up a couple of months now. This guy still likes me and we flirt like crazy, and they aren't back together but I don't really know what is happening between them. So my question is what should I do?