Replying to Bro's before hoe's?

So this thread is a little pointless but i just wanted to see what you would do in my situation.

My buddy starts dating this girl, a month later he dumps her after cheating on her. A week later they get back together within a month he cheats on her again and dumps her again. A couple weeks later i find myself talking to the girl, she asks if i want to hang out sometime im down for it, shes cool and i dont think my buddy would mind because he dumped her twice. Me and the girl hang out for about 2 weeks with out my buddy knowing. Then he finds out and flips shit saying that i need to chose him or her and that i am being a terrible friend? overall im just pissed that i cant hang out with the girl with out potentially loosing a friend.

so NS what would you do?