Always keep him in your heart. He would want you to be happy. Letting go doesn't mean forever forgetting. You need put yourself out there. Start dating and meeting people. Even just making friends. I am sure if he could tell you. He would tell you to be happy. Keep a spot in your heart for him. Just don't chain yourself down to it. No one wants that for you.
I don't have a definite answer for how to get over somebody. In fact, I'm trying to face the same problem myself. What I think has worked for me is changing the unconscious thoughts that remind me of the person I'm trying to get over. What may be troubling you is you're still thinking about the man you lost and reminding you that you lost him. To not think about him so much, you have to dissociate him from most things you do. Avoid listening to songs that remind you of him, if you can help it. Don't go to the places he would take you. If you can't dissociate him from certain things- since parts of your school could remind you of him and you can't stop going there, for example- you could try to one-up the idea and associate that kind of stuff with other things. Look for funny videos talking about movies you've watched with him (so you think of the funny video instead of him). Listen to cover bands singing the songs that he liked instead of the original artist (so it sounds different enough to you to be almost like a different song). In the end, you'll grieve a lot... and that's normal. The point is to grieve with purpose. It's not very poetic, but I think of the quote, "The purpose of a funeral is to let go." (Or something like that.) It's okay to feel bad up until you find a way to move on... as long as you don't stay attached to him after he's gone. I wish you the best. And I hope my advice helps you somehow.