Hello Chelle, I don't have any answers for you as I have been unable to find much support for men in abusive relationships in the UK. I have a male family member in what appears to be an EA relationship, and I would love to be able to offer him somewhere to turn to when he is ready.
It's hard. I think you started a thread earlier that I posted on? I guess it's a fine dividing line between interfering and supporting. The last thing I want to do is push him away by insulting his girlfriend/relationship because he may not be ready yet to step away. I think this is the case but also think he is getting close to start making moves.
As with anyone in an abusive relationship the key is generally not to criticise them or their partner. To help them take control of their own life again by guiding them to form the correct conclusions about their partner's behaviour themselves. Listening to how they feel, asking how things make them feel and encouraging them to talk rather than steaming in with accusations/advice.
That and signposting to appropriate organisations like DA support above and CAB for practical advice on ending a relationship when they are ready.
Also although Lundy Bancroft uses the male gender for the perpetrator and the female gender for the victim, it's worth noting that the patterns are the same. It might be helpful for him to read anyway, if you think that he wouldn't be put off by having to mentally switch the hes and shes around.
Men tend to hide the abuse, especially if it's physical. My brother had to call the police, who were great (this was Australia). They told him that it will happen again. They separated for a year but are now back together. They still have a stormy relationship. My other brother said it's very painful listening to them argue - they were only staying a couple nights at my mums. But what can you do? She seems to have a huge hold over him. They are both professionals.
Everyone tends to hide the abuse tbh. Part of that is that most victims of abuse do not think of it or properly recognise it as abuse while they are under the control of an abuser. The abuser tends to control the victims perception of events, the victim usually suffers anxiety but usually internalises the abuser's narrative as their own.