I/ we don't know what to do...need help... quickly please:/

Hi there.Me and my girlfriend are in a relationship for almost a year, it started as a long distance relationship between Germany and England but we closed the distance last month and I'm living with her now in the UK.She really is the love of my life and she's the most important thing and most important person in the world and I would do anything for her - she's the only thing and only person I need in this world. But let's get to the part where I need some advise from you guys. My girlfriend was on a party last weekend and I always feel a bitt worried be for she leaves which I also tell her every time. And this time my worries were proved...unfortunately:/ so there is this guy which fancies her a bit and he was on that party. But he talked to my girlfriend the last few days for advise to meet with a girl which my girlfriend knows, so she might fancies this other girl too and that's why my girlfriend thought that he might stop with talking to her at the party too much...which didn't happen.

It was 1am and we went to pick my girlfriend up from the party, then we got home and she started saying randomly 'sorry' , I asked what happened but she didn't say anything cause she was scared but I know my girl and then I knew something bad happened... I comforted her and asked again and then she told me. Because all of the people at the party have been pretty exhausted and tired all went to sleep at around 1am. My girl was laying in the hallway with some of her friends and this guy and for some reason she just used one of his legs as a pillow (she was still a bit drunk) but then he started touching her up in the face down to her breasts, sometime people stepped in and saw it and then he always stopped and acted like nothing happened. As soon as they were gone he started doing it again. And then the bad part starts...he took her hand, put his trousers and boxers down and made her touch his dick ( he also tried to push her head down there which didn't work well). My girl was acting like she was asleep so she didn't move at all, everything that happened was because of him. She didn't know what to do because she was shocked so she kept acting that she was sleeping , which was a good idea in my opinion - I probably would've done the same in that situation. When we were laying in bed she showed me where he touched her up and sometimes when I touched some areas like her neck she was thinking about it and looked a bit scared and also told me 'that's what he did'.
So two days after all that I can't stop thinking about it. Every time I touch I'm scared she is scared again or that it reminds her what happens. I'm also not feeling like to have sex too soon, because I'll think that my girl might think its his dick:/
Me and my girl just need help for that case? Maybe you guys have some advise for me/ us.
And I don't know what to do with the guy... I wanna send him a message to **** off and stay away from her, but my girl doesn't want it because she's worried it will cause a scene at college because he's on the same college as my girl in the same friend group, the good thing is that my girl is ignoring him and stay's away from him. But I feel like that I have to tell him to stay away and to let him know that I know what he did. Another thing is, I'm not sure if that what he did counts as sexual harassment, so was also thinking in contacting the police.

I / We just need help from you or just some tips for what I /we could do now.

And I apologize if it's a really long 'essay'.
It's just so important to me and I wanna get it sorted as soon as possible and I out of my head as soon as possible.

Thanks to all of you for help, I really appreciate it.

If thats how it happened, Its not sexual harrasment ,It's plain and simply sexual assault. If other people witnessed this then there should be no problem proving it either if you did go to the police. However your girlfriend may not want this and it should be a joint decision if you are going to take action otherwise you risk damaging your relationship.

This guy should not get away with it, personally I would have probably lost my head and probably done more than warn him. One thing to make sure if that your girlfriends, friend he was talking to her about does not go anywhere near this guy.

I am more conservative about these things than the previous poster, so what I am going to say might hurt, but will ultimately give her more power in the future and will enhance her personal safety. It will also reduce future drama.

Your girlfriend needs to make her words and her body language match. She should not have been laying on a male she wasn't interested in (drunk or not, who does that?), and when he began to touch her, she should have told him to stop. Why do you assume that other guy thought she was sleeping? Your girlfriend knew he was interested, and voluntarily initiated physical contact.

Also, it's an old saying, but "nothing good happens after midnight". If she wants to go to a party, fine, but why stay past the time when all you can expect is trouble?

Also, maybe your girlfriend should drink less so she can be more capable of using better judgement.

Trust me I lost my head that night, I thought about doing the worst things to him but I tried to stay cool and thoughs its never good to do things with too much emotions. And I'm also gonna send him a message later, because I talked about it with my girl earlier and she also said that all of the friends in college know about it too already. Let's see what else I'm/ We gonna do with him.
Thanks for your help.

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These are things we already talked about together and we sorted them. I told her to drink less, to stay away from boys, not to go to parties where he's gonna be and not to stay too long.
Also thanks for your help.