Iforget, you have a lot in common with my daughter. She, too, has a brother with deep problems. She, too, has it together and is building a lovely family for herself.
I like to think that my daughter and I have found the right balance of love and care for my son. He gets our love, our encouragement, hope always, and free advice. We have put limits, however, on how often he can call. Sometimes he has anxiety attacks and calls many times in the same night. For our own sanity, we have limits on that. It turns out that he is quite happy to stay within those limits, because his relationship with us is so important to him.
Outside of that, it's his life and he has to fix it.