I'm very glad to hear the support is reciprocal. Once again, I can't ever speak for your friend, but in my own life the dark side of relying on other people to remind you that you're human is that it's possible to let resentment to build up toward them for exactly that. It's hard to describe, but the way mental illness cuts away at your ability to self-determine on a day-by-day, moment-to-moment basis can make anyone profoundly and uncomfortably aware of the power dynamics in any relationship, even one based in honest charity, so any kind of reciprocity is a *hugely* good thing.
I wish I had more advice on what you can do for your friend, but anything further gets into tricky territory that you would know better than me. I'll leave you with two last thoughts.
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1) If you think he'd be open to talking about his current therapy situation with you it might be something to give a try, if you can find the right moment, and just so long as you're coming to him as a friend and not a life-coach. It's a real tricky line to walk for anyone, but it sounds like you're a pretty communicative pair when you're in touch, and that's what's most important.
Anyway, what I was going to say is that if he's out of therapy, or in it but making no progress, you might encourage him to reconsider his options. Many therapists are, to be blunt, only equipped to help people with low-level emotional problems, whatever they might say. Finding the right match, one who can really help someone tackle a severe and chronic disorder, takes a good bit of online research, asking tough questions about their approach and history in the intro appointment, and being willing to shop around if need be. But is definitely worth it.
I've found the best way to find a good mental health professional of any sort is to ask other local mental health professionals for a recommendation, perhaps one at a college or local research institution. I'd even suggest even just emailing them out of the blue if your friend doesn't have any contacts. People can be surprisingly open to that kind of initiative.
2) If his worst OCD symptoms come about in very sudden and highly intense relapses, and especially if he's every noticed any connection between them and getting an infection, you may want to ask if he's heard about an autoimmune disorder called PANS or PANDAS. It's a pretty new frontier of research, but if he does chance to belong to that (admittedly very small) sub-group, then I speak from experience when I say that traditional therapies may not do much for him until he addresses things with a specialized neurologist, rather than a psych.
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And with that I think I'm pretty much tapped out for advice, unless you had other questions. Best of luck to you both.