If He's The Right Guy Then What's Wrong? (Help)

okay so I'll start from the beginning:

I was hurt by my ex about a month or so ago. I was on and off with him for the whole school and he always switched between me and this one girl and he finally went back to that one girl and they're in love now or something. I'm so much happier without him in my life- I was put in that situation where I can't even be friends with him anymore.

And 2 weeks before school ended I meet this one guy in one of my classes and the first time we talked on the phone for three hours. I found out that I have a lot in common with this guy and we talk on the phone just about everyday because I'm out of state right now. He says he likes me a lot and he's what I've always wanted- he can keep conversation with me, he's really nice and he says he likes me a lot and he always makes me blush, and he's an athlete (well thats not something I wanted exactly but just randomly throwing that out there). Overall, he's waaaaay better than my ex.
The last time I saw him I kissed him (just a simple peck) goodbye and I said I was going to miss him...
but I'm not really sure how I feel about him right now. When I was feeling unsure last night and I called him we were on the phone for like 3 hours of course and I like talking to him, but I don't know what's wrong.
I have this tight feeling in my chest that I think every girl gets when they think something isn't right (I dont have this feeling while I was talking to him though)
I don't know if I'm holding back because I was emotionally damaged from my ex or if I'm just not the type of person for relationships.
and I really don't want to hurt him, I want to give him a chance and I'm pretty sure I will, but I don't know why I'm feeling so confused about him.
If he's a good guy- which was all I wanted- then why do I think I don't want it now?
I think I obviously have feelings/care about him if I'm so worried about hurting him, but I don't know.
I don't understand what the problem is...

ps. did I mention one of my other exes wants me back...he's not exactly the right choice (he cheated on me) but it doesnt mean I have tempting thoughts >.>
gah!!!