Kb, I don't believe there is anything you, or anyone else, can do to hurry it along.
It will need to come from him. As irritating as that is. When he is really ready to face the reality of what he has done, I expect he will.
Sometimes it just takes a small thing to send them into depression bad enough to want to change.
Sometimes it's something big. No one knows what causes them to go into liminal depression, but you would see it.
It is a dark place they go in. Not just your normal MLC depression.