DH and I have a friend who is regularly being beaten up by his girlfriend. She started by throwing a few punches his way when she was drunk, every now and again. This has escalated - last weekend she saw him on the dance floor talking to another girl, came storming over, grabbed him by his hair and punched him in the face several times.
Every time, he comes to my DH for advice, maintains it is 'make or break' they are going to work at their relationship, and things go back to normal again a few days later. They live together, next door to her parents which makes it very tricky for him to extricate himself.
The nature of his employment is a very 'lads' culture - meaning that he is basically torn apart and teased massively for being attacked by his girlfriend, for example his colleagues tag him in Facebook memes all about his girlfriend being more 'man' than him and so on. Now he goes along with this and laughs and then changes the subject, but really I imagine he is devastated and trapped and can't get himself out. I don't know how we can help him. Any ideas please?