My Dbro was a victim of violence - wouldn't think it - big bloke and used to box. But she abused him mentally and physically
he wasn't allowed to talk to his twim sister or my parents. he got in touch with me, when he though the only way out was to drive into a tree. All I could do, was to listen, offer him love and shelter, and for a while he was back and forth from my house to her (60 miles away).
I tried hard not to say anything at the time but I was so angry
.
When he stayed with me I showed him there was more to life that the narrow existence he was living with her - not allowed to watch TV or read newspaper, she would watch him at work to see who he talked too. I encouraged him to apply to Uni, (actually I took him to the applications office and filled the form out for him!) Once he settle in, with me and uni he told me everything that she did, I wanted to kill her, from that moment I went all out to help him to get her out of his life - he might not have exactly wanted my help, but I told him 'you can't tell me things like that and expect me to sit back - would you'.
it helped that she kept promising to change, but after several false 'restarts' she didn't.
Violence in any relationship is wrong, he never once hit her (felt like it) and I wouldn't be happy with him if he was violent towards a partner.
With your friend, it's a delicate area, but maybe he told you as a plea for help. There are organisations that he could get in touch with.
It will help him if you are there for him. Hope he gets things sorted.