I need help remembering this book series?

i read it when i was younger. i cant remember what its called or really what its about but i know its about a boy who is like destined to save the world because he is something and i think he travels through time or different worlds. In the first book when he finds out he has this destiny he is with a girl whom he feels he is leavign for good or something. its driving me crazy that i cant remember. please help