...Really? You really have to ask us how to feel about this?
Okay, fasten your safety-belt while we examine and highlight the key points of this post....
^ There you have it. He obviously was bullshitting you if he told you he's getting too attached and doesn't want it. The way he just jumped back with his ex means that he wants to get attached- just not with you... On top of that, any self-respecting guy that wants a relationship and does not have issues of their own would jump at the idea of getting attached to their significant other. This means that he's not only a liar but that his relationship with you didn't seem to mean too much to him, especially because he moved on so quickly.
So, in short, you should be applauding his ex for taking a lying child off your hands. She did you a favor, OP, as hurtful as it is to hear.
What do I recommend you do now? First of all, get some distance from that prick and think about how much he's hurt you by ignoring you. Think about how completely inconsiderate and how contradictory his reasoning for ending it is because he obviously didn't waste any time between relationships. Second, you have to take time to cope and focus on yourself. Do the things that you like to do. Go out with friends and have a good time. OP, this is even the chance for you to go and make new friends. All you have to do during this time is let yourself heal. And third, once you do heal, grow from this and don't let any guy push you around like that again. Ease back into the dating pool and search for someone better who won't ignore you and treat you like something he can just throw away. Because you know what? You're worth so much more than that.
I hope this helps. Best of luck.