Stop hooking up with him. Ignore his booty calls, booty texts, booty IMs, booty Facebook messages, booty Tweets. This guy's a scumbag for keeping you on the side while also dating someone. He called you up for sex and then suddenly gets a conscience and doesn't want to cheat on the new girl he's seeing? Ugh. Who does that? Why did he call you up in the first place? On the disrespectful scale, that's a 10.

I'm assuming the girl he's seeing called or texted while you were on the way over, and he suddenly decided he didn't want to be a complete piece of s--t to two women. It's hard to accept, but he clearly has more respect for the other girl than you. Right now, you're his fallback in case things with the "lady friend" turn sour. Thus, the calls and hints about fooling around. My guess is she doesn't know about you, which makes things even worse. He's seeing someone but still keeping you in his back pocket. Why do you want to be his, as they say on Boardwalk Empire, "back alley Betty"?

Clearly you have feelings for him if you're at all conflicted after the way he treated you. Now that he's seeing someone else, do you really want to have anything to do with him? It doesn't sound like he's a very good friend, or interested in you for anything other than sex. This isn't going to end well. Either he'll cheat on the girl he's seeing with you, or he'll get serious with her and you'll get hurt. You might not want to admit it, but you have feelings for him. The smartest thing you can do is to cut him out of your life. Is it even worth going back to being friends? He doesn't treat you very well as a friend or a friend with benefits. Why does he deserve to be either to you? Stand up for yourself and end things immediately. Also, feel free to let him know what a massive douchemonkey he is.