Hi Tangled.
You beat me to mentioning GSA...good for you on researching it.

It is, according to what I've read, a real (and apparently very...persuasive) thing, but I can't speak to what extent.
I applaud your attempts at understanding...you're a better one than I am for that. I don't think I could. But I do share Kaliope's concerns...there is a limit. He needs to stop this, immediately. Granted, I'm speaking to something I don't know the full extent of (I don't know enough about GSA to say how much sway it has over an affected individual), but he should take steps to get some help. I do completely understand his hesitation in admitting this to a therapist, but he needs to get professional help. I don't think this is anything a therapist hasn't been trained to handle, and he shouldn't feel embarrassed in confessing it. The therapist is there for a job, at the end of the day...he won't be judged or anything of that nature.
On the plus side, I think he realizes this is wrong...his confessing to you and his confession about his guilt to you speaks to the fact he *does* realize what he's doing, but is perhaps unable to stop. Perhaps like an addiction of sorts? Regardless, if he's thinking logically about it and *knows* its wrong, it could be an indication he could be persuaded to talk to a therapist.
Hugs Tangled. I wish you all of the best as you work through this.
Hugs,
Harley