I do not know what to do with this guy and his ex-girlfriend. Insight please!?

I have been talking with this guy for two months and so far everything has been good. He hasn't lied but he has tendency not to fully explain situations, especially when it's a dramatic one. His ex-girlfriend recently messaged me on Facebook, saying that they have been going out for a year and a half-- on and off. Basically, she wants to get to the bottom of this. He claims that she's psycho and that she does this to get a rise out of people. She claims that she is the only girlfriend in this and that the guy has nothing to do with me, apparently. He calls and texts me, apologizing. I ask for a further, more detailed explanation and he says he will call me later. It has been about 4 days since I last spoke to him and he says his reason for being absent is because he has midterms and a project due. I feel like he is avoiding the situation and he also claims that they got into a huge argument and that he isn't even speaking to her right now. SO WHAT TO DO? Should I leave him alone until he contacts me again or should I take the initiative to contact him and get to the bottom of this?