Seeking wisdom from the petty goddesses.

So I was seeing this guy who had just broken up with his gf of 3 years. It seemed like we were getting along great & there was a chance of actually forming a relationship. Instead he says he does not want anything serious. This was really disappointing to me. Just last night he messaged me & told me he was getting back with his ex. This morning his ex or now current gf sent me a friend request on instagram. I don't know if I should accept her or not. What would you do?