I'm not really sure what kind of advice I'm expecting,

Sadly not enough info, even if I was a professional psychotherapist, the situation is so delicate that you would need to write an essay on the details.
It's possible that you wrote this, because you know someone would suggest that he not see his family for a while. There is nothing wr.ong with that, in both senses.
If you want, we can talk about one problem that he relapses on, and get advice.
Obviously from a big picture perspective, dude needs to take a fucking break from his family. You might want to consider that advice might be better given as to how you can learn to fight for that successfully.
Frankly it sounds like a cycle, a merry go round, I can paint a horse but what the fuck will that do? We might want to think about shutting down the ride.

>>17884932
He has never been able to say no to his mother. If he says no, and she sends him on a guilt trip, and he capitulates. I don't think there's much chance of him "getting off the ride" any time soon.

Is there anything that can be done to help him spring back more quickly, or not lose as much ground?

If describing problems would help, I can do that a bit. He's got severe anxiety issues, mostly socially, and OCD. Before he goes on one of these trips he can act pretty normal, even if he's stressing. When he gets back, he won't leave the apartment for a week without panic, and the OCD is back in high gear. He apologizes for everything he does, and for not doing everything he doesn't do, and tenses up if I touch him. He picks the skin off his fingers and hands. He won't sleep for more than a few hours at a time, and won't work out or eat regularly.

After a week or so he starts to calm down, but it takes quite a while for him to get back to how he was before visiting.

https://www.youtube.com/watch?v=Iw3sDgaoBeA

This is beyond advice, this is clinical. He has rigidity , You can play some shit on the big speakers (if you have them), things like this video reduce rigidity.

Also when he panics, he is likely scared of what is going to happen next, and this makes him panic even more. You can remind him that he has panicked before and the world didn't end. The anxiety is him reaching into the future, and seeing something bad. But if you could show him that the bad thing doesn't happen (his panic episondes always just end with normal life) then the panic will be reduced.

You need to know that, even this little stuff that I am suggesting, is not your responsibility. You are never obligated to rescue anyone, and you are fully entitled to your own life.

This whole fucking situation is not of your doing, you didn't create it, it is not some message from fate that you owe your dues (or whatever). You can choose to get out at any time and you are in no way a bad person.

Not even experts can solve the problems you present at any reliable rate, so to beat yourself up for anything, and I mean anything, is not only wrong , but doesn't actually help a god damn thing.

You are in a deep quagmire,

I'm definitely not going to leave him. When he's got this stuff under control, he's amazing. It's just heartbreaking to see someone like that suffer so much though. He doesn't deserve it.

No relationship is perfect. This is the imperfect part of this one.

>>17884932
>Obviously from a big picture perspective, dude needs to take a fucking break from his family

This. Making huge assumptions here, but it sounds like his family is toxic.