I'm not sure if this is something that a person gets over. I think its just easier to handle with time. You will always miss him and situations will come up that would have been perfect or remind you of him or that you thought he'd be around for. The only thing I can suggest is remembering the good things. Maybe worked towards something to honor his memory. Something that makes you feel good while remembering him anf this could be something you share with him in spirit. Its weird to explain I guess, and everyone would need to find their own way of dealing with things, but.. Remembering him isn't bad. Try to let go of that feeling. You shouldn't feel sad when you think about him, you should feel happy or proud, always enjoy his memory.