I think he is just using you to make the other girl jealous. Anyway, keep away from him. Rebounds are never a good thing.
I would thread carefully. It sounds like in his eyes he believes that the other girl is his true love and that anyone else is short.
Well, if he's using words that he admires you and thinks you have a beautiful heart, it's not revealing the most important factor. Does he find you attractive? Maybe all these sweet gestures are a way of avoiding saying this?
I am just saying to be careful. He sounds like he is definitely the type that would avoid saying something/lie to avoid hurting your feelings. Do you see that in him?