So, we were driving for a night out last night with friends we have known for 10 years. I'll call them Matt and Laura
No inkling anything was wrong then some muttering, then all of a sudden an outburst. Matt spouts the most vile language full of venom, I mean awful. Then punches her in the arm 
We turn round and come home (they live near).. as we pull on the drive Matt gets out.. Laura stays in the car.. as he walks round the car she flinches because she thinks he is opening her door. She is terrified. He goes to there house.. we take her into ours.
Laura admits this isn't the first time.. but she loves him and he's a good man. No one knows but us. She is determined to go home although we offered her to stay with us. so I need to ensure she is safe. I go round to theirs, talk to him. He doesn't know I know about the violence and I don't let on because Laura tells him he will be angry and I can't risk Laura's safety. He comes round to ours, still element of angry... I am sat there trying to sort it so she is safe listening to his woes and why she was wrong to trigger his temper 

She is coming over for a cuppa in a bit, I need to help her but I'm at a loss because 'she loves him and he's a good man' 