That sounds very challenging. That sounds like a true nisyayon. As others have suggested, try speaking to his rav/mentor (unless of course, you feel that would be counter productive). Just know that this unfortunately isn’t as uncommon as you think. I heard a shuir by R’ Shaya Cohen of ZA who mentioned that he’s dealt with many adults in families that go OTD. I recommend you try to contact him if you can.
Also, I’m not sure why some are jumping to the conclusion this is internet related, but if it were, that wouldn’t mean that he’s “going OTD.” If someone chas v’shalom struggles with holding themselves back from speaking lashon harah, we wouldn’t describe them as going “OTD.” That’s just called the yetzer harah getting the best of them.