Let me express how sorry and embarrassed I feel (as a male) that you have been put under such stress for no other reason than being a young female, which behaved exactly as some her male co-students would have done (socializing on a faculty party).
There are In my opinion 3 aspects of this: Professional/etiquette, Legal and emotional. I wont discuss about legal, since you were not specific on the country and specifics of the harassment, and since I feel that this is not the direction you want advice. I will skip emotional, because to judge what has happened I don't need to understand the emotions behind. For that I have to say it does not contribute if you (seem, pretend or believe) to like each other (in one direction or two) or not.
Let's gather the facts:
- He is your supervisor - he has the objective power
- He is an employee, he gets paid for his work, and you are a student. In some sense, his customer.
- He is older, in an environment where he believes that it's acceptable to get sexual with students in the presence of other teacher and students (This tell me that something is wrong with the faculty ethics there) - he has control
- It seems normal for him to have relationships with his female students, who are in a insecure emotional state of transition - if that is a habit, it is clear that he is experienced in abusing his position (This again tells me that something is wrong with the faculty ethics there)
- I could imagine that something like this incident would have been a misinterpretation of him, but in that case, i would have expected an sincere apology towards you
- It is clearly unacceptable from an etiquette viewpoint to skip hugging and other more personal forms of interaction in a social relationship and wait until the other person is drunk enough to touch him/her in a sexual way.
So these are the facts as I see them, and my summary is clear: He behaved unprofessional, irresponsible, and as it seems intentionally abusive, with a lack of professional and interpersonal ethics. While you being drunk may have allowed him to do what he did, the failure is on his side.
I reinterpret your questions to:
I have a supervisor, which seems to be intentionally abusive if he believes he can get away with it (and I assume that this may be true). Given the asymmetry of power, what is the way with the least further harm for my life to get away from there and avoid future harassment for me from such nonprofessional and abusive people.
- I assume that he is not emotionally involved in this (given his history), so there are good chances that he at least does not take your "rejection" personally and has some hidden issue with you (and e.g. takes revenge when grading). So I don't expect his behavior to be a recurring thing (towards you). However, if you have the feeling that the grade of your work was affected by it (or he make strange remarks indicating that he expected different from you), you should evaluate further steps.
My first advice: Try to walk away from it as unharmed as possible, as a student in a university you will fight an uphill battle in such contexts. Clearly separate you own good (getting away with a decent grade and without being harassed any further - if he tries it, walk away directly and go to the faculty) from the good of the others (i.e. telling the responsible person at the University about this - possibly do this later, after getting away.). Don't let people tell you that "women are at fault because they would need to go after such persons stronger" - in such a situation it is not your responsibility to clean up other peoples mess.
The second advice (as much as i hate to give it to you in this context): The world is full of seemingly nice and close people (students, teachers, colleagues) who lie to you, and will exploit your weaknesses. Some people are psychopaths and these are very good liars. Getting drunk (since it weakens you temporarily) among people you don't know is not a good idea, so only get drunk with people you know well enough.
The third advice is: look for the publication record when selecting a supervisor. If you see a stable pattern (e.g. Master students which are still there as Postdocs) of coauthors around him/her on the articles it means usually that he/she does not cause people to run away for emotional, sexual or other (workload) abuse.