If the one you love doesn't want to be with you....?

I posted a dilemma a while ago.... my boyfriend of 4 years split up with me when we got to Uni and i started seeing someone else after a couple of months of heartache. After 6 weeks of a new relationship I had to follow my heart and realised i am still totally in love with my 1st bf, I decided i wanted to forgive everything he'd done to hurt me. We started going out but i had a few trust issues with him so didn't want to rush into things, now i KNOW we're ment to be, but he's decided despite the fact he loves me and wants to be with me 'one day' he's not ready for a serious relationship at the moment. I love him more than anything.... all i want to do is be with him.... i just can't understand if he loves me too why we can't just go for it?? It's tearing me up and it hurts so much. What can I do?? I know i want to be with him more than anything......