<human>: Can you summarize the given text in a few sentences?

My sister is a 19 year old student at university in the UK, last night she went out with a couple of friends & one of the girls boyfriend who was visiting. They went back to their halls & sat in her room chilling. They sparked up a spliff, which made my sister whitey. While she was being sick, the boy (I say boy, he's 28) was rubbing her back and comforting her. The other girls went into the kitchen, he started grabbing her bum which she moved away from. He then tried to reach down her top, she moved away and put her hand over, he grabbed her hand out the way and put his hand inside her bra. She jumped up and ran out the room in tears....

It ended in a bit of a confrontation with the girlfriend crying and the boy calling my sister a drunken slag! She wouldn't make this up, she keeps blaming herself for being in that state, but he took advantage & surely that's sexual assault!? Because it's her best friends boyfriend she hasn't done anything about it, I want her to report it to the security where she lives and get this scumbag banned from visiting her halls...she should feel comfortable and safe in her own home! And if he can do that to his girlfriends best friend, I worry what he might do to anyone else! She keeps saying she doesn't want to lose her friend over it.

I don't know what to say to her, I'm so angry and upset! Also living on the other side of the country so feel pretty useless...
<bot>: my sister was drunk and being sick, best friends boyfriend felt her up and put his hand in her bra. Sexual abuse? She won't report it.