<human>: Can you provide a brief overview of the text?

Been with this girl for two years, everythings great, communications easy, sex keeps getting better and everything is peachy. I come from a very loving family with very very few rows or confrontations, whereas hers is the opposite. Her dad has anger issues and is abusive and her mum is an alcoholic, though she's lovely when she's sober. 

I've never really clicked with her dad and he's been a real prick to everyone in the family. Blowing up for no reason, pouring water over the mums head in the middle ofthe night. While i didnt like what he was doing in the slightest i tried to keep an open mind because he's my SO's dad and our families are just polar opposites. 

This weekend however my SO told me that when she was 15 her dad went berserk and I assume beat everyone but he definitely hit my girlfriend. Now obviously this makes me beyond angry, but I still have to see him over Christmas. Everytime I think about going over to the parents house I just get this image of my SO being punched and flying across the room defenseless and it makes my blood boil. He's apparently swung for her again, most recently about 6 months ago but she just stayed at mine.

Can any one give me any insight in to how I can deal with this? I'm just so unused to any confrontation, physical or verbal in families. Also how do I support my SO whenthis could easily happen again?
<bot>: so's father is physically abusive, known for a while he has anger problems but only just found out he's hit my SO. How do I deal with being in the same room as him and how do I support my SO?