Welcome. I hope that you can find some of what you're looking for here.
Yes, it is a shock to hear about. Yes, it makes you feel powerless, confused, afraid. You feel that nothing you can do could possibly counteract all those years of pain. Maybe you've heard some other things that don't elicit such easy sympathy and you're afraid to think about how you feel about those things.
I'm pretty new here too, and I can tell you that a lot of the despair, anger, sorrow, etc. that you feel now doesn't go away, but very soon it stops being so crippling. That's because, as you've said, we want to know what we can do. And we want to do it.
I think the first and most important thing, which I've said on this forum already, is that while I told my boyfriend that I believed him and took his emotions very seriously, and would listen to him when he needed it, I also made sure that he knew that he was the same guy he'd been before. We went out and did the things we always do, we laughed, we bickered about doing the dishes. I didn't burst into tears when he walked through the door, thinking about his sad life all over again (I cried and cried but not to him). I didn't tiptoe around him. I didn't start sleeping on the couch. I didn't kick him out, I didn't call all of our friends, etc etc.
I didn't do any of that and I wouldn't have, but I didn't know until I started reading the posts here, how real all of these fears are to the men who disclose to their loved ones. They don't want to lose their loved ones, and they don't want to poison their (less un-) healthy relationships with the hate and hurt of their abusive relationships. As irrational and even personally insulting ("But I'm not that person; doesn't he know I'd never do that...") as these fears seem to you, you have to let him know that they are unfounded.
You also have to make sure that before you start talking about self-destructive modes and counseling, that HE is the one who recognizes and wants to get out of his self-destructive mode, and that HE is the one who wants to get counseling. You don't have to go far on this forum to read about partners and friends who try so hard to make someone see that their point of view is the right one. I'm guilty of this myself at times. Usually it ends badly.
Good luck. I hope you decide to read and post more.
Sar