Im deeply sorry for your loss.
It hurts even about thinking about someone you love dieing...
If I where him before he had died... I would have treated you like shit. I would broken up with you, pretended I was some fake bastard. Why? That way you wouldn't get as hurt as you are know. You probably wouldn't have known he would die if you two would have broken up before. Trust me. It would have hurt less that way.
Sadly you can't do anything about it now.
If you're like religious.. I recommend you pray to him everyday. Think about him. Errr... but don't think of him as an option or as a boyfriend anymore. He's fucking dead. Try getting that through your head. He won't be coming back. If it helps, find someone new. But don't automatically stop thinking of him... But just don't think of him as a bf anymore and all longing for him.
Truly ^^that's^^ all you can do. I mean I'm sorry you lost him and it's definitely a bitch, but you've got to move on. You can't bring him back and there's no use morning over him forever. Again, I'm really sorry you did lose him though.