Yeah I kind of have to side with Flooded. You really just shouldn't waste your time with this guy even if he is "newly single". It really wouldn't surprise me if he ended up back with this girl, though. For right now he's probably testing the waters, hoping the break-up would mollify you and make you come swooping into his arms. Then he may decide to take her back and try to have you both AGAIN after he butters you up for a bit. I'm not saying that is what would happen, but it sounds like he's not entirely let go of his relationship with her either. And it sounds like he is just that sort of person from what you've described.

I'd suggest you write him off entirely and focus on yourself for a while before you even begin thinking about relationships. I know it won't be easy and I know it will hurt. But you are compromising your self-respect every time you beg for a sliver of attention from this boy. He doesn't deserve your regard. You deserve a guy who will make you number one from the get-go. And, as others have pointed out, look at the way he has treated his girlfriend. Put yourself in her shoes for a moment. I'm not doing this to make you feel guilty, but just think for a moment about how he treated her. He was utterly disrespectful of her feelings and her as a person while they were in a relationship to say nothing of how he treated you when you two were not in a relationship. Do you really think you'll be any different to him should you two become a couple? I just wouldn't trust this guy at all.

Whatever choice you make, I hope it's the right one for you. Best of luck!