Maybe you could offer to cook something and see if he'd like to invite anyone over? My wife offers to do that sometimes since I have become a hermit.

Would it be possible for him to disclose to some of his friends? Even if they are friendships that are more focused on doing things rather than long involved talks about feelings and personal lives, it really helps. Even though I rarely discuss the assault with the friends I've told it is good, I feel less of a fake around them. I don't feel like I'm pretending I'm someone I'm not the entire time. That is very therapeutic for me, even though it doesn't look like "recovery work"
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“If a man wishes to be sure of the road he treads on, he must close his eyes and walk in the dark.”

- Saint John of the Cross