Can he or will he? That's the real question. Does he even believe there is a problem. Maybe he has other reasons for avoiding marriage, if that's what he is doing. What makes you believe he can't or isn't getting over it? Have you asked? What does he say about his parent's marriage? If he can't get a grip on it he may need professional help. Is he even interested in marriage? Can you wait for him to get insight?
Probably. Divorce can be a very traumatic experience, especially if experienced as a child. Those adversely affected by divorce should seek professional help (family doctor, counselor, psychologist, or psychiatrist) so that they can work through these issues.
Parent's divorce. Sounds like he needs to explore not only his fears of marriage, but what happened to him back then as a child as a result of the divorce. I'm optimistic that if he commits himself to doing this for himself and you, there can be a successful outcome.