I re-found this thread, and I thought I'd try to answer.
He disclosed to me as we were breaking up. This was about 8 months into our relationship. I think he was ready to share, but I definitely pushed him, because I just didn't understand why he was ending our relationship - especially while also telling me how wonderful I am, etc. He finally blurted it out, when he couldn't keep repeating the excuses for breaking up anymore.
My reaction, I think, was one of support. It clarified so much for me. It was a huge relief. I knew that something had to be wrong, because I couldn't figure out why he kept pulling away (and was now breaking up with me), particularly after a great weekend together. So to realize that we were breaking up because of something larger than me, and it wasn't my fault - that was huge for me. It was important for us both to recognize, and it allowed me to be sympathetic and supportive, rather than a mean, slighted ex-girlfriend.
Since then we got back together, broke up again, got back together, and most recently, broke up again. I do think its over for us, at least until he deals with the abuse, takes care of himself, etc. mostly because I just can't keep going through this cycle.
But I have to say this, we most definitely would not have made it as far as we had, if he had not disclosed. He would've pulled away a long time ago - and I would've let him, hurt that he was being mean to me, causing me pain. Knowing the truth helped so so so much. Even in this breakup, I know that it doesn't have to do with me - and that knowledge is what is going to allow me (hopefully) to move on sooner.