I understand your frustration. If you don't feel you can properly DB or have the motivation to do so any longer, perhaps you just need to go with the Tough Love/Letting Go approach. It can be very liberating for yourself and can also provide exactly what is needed to motivate the wayward back into the M. Basically, it's similar to the going dark part of DBing... a little different in nuance.
You're right though: H won't grow up or get help to grow up until he has sufficient motivation to do so. Having said that, none of us can say with certainty that any situation is without hope! Even professional therapists can't tell you that.
