That's a total drag Randy. I've had friends drift away and others who abruptly disappear. The second is painful, especially if they are doing it because of a relationship.
You obviously don't know all the details of his disappearance, but speaking from experience, if in 5 years your friend approaches you, be the bigger man and try to forgive. Maybe there is something going on with his life (or relationship). Not making an excuse for him, but it may take him time to figure it out.
If he doesn't make his way back, its sad, but you have no choice but move on.