Sin of that nature is between him, his wife, and his God.
Were he a friend in such a circumstance, I would simply want to remind him of what the first category demonstrates.
I have taken this sidebar in our discussion of Joshua Harris because it is important that Christians understand that this is where he falls.
Had he taken to Instagram to announce, say, a personal failure that led to his divorce, I would be the last to condemn him, not the least because his sin is not against me and it is, really, none of my business in the first place.
They trusted God and ran to him as they stood on the edge of their self-made abysses.