Depressingly, Yorick is right that this actually has a name - it's called motorboating. I've worked in a student advice centre, and this was a common(ish) type of sexual assault at student nights. Yes, it is usually some bloke who is immature, drunk and is doing it "for a laugh", but that is absolutely no excuse whatsoever. It is sexual assault, and despite what some posters above have said, it is taken seriously by the police these days. In my experience with my students, the best way to deal with this initially (if you want to do something) is to speak to the Club and tell them what happened. Decent clubs have a zero tolerance policy, and if they have CCTV, or know him as a regular, they will be able to do something. For general info, if something like this happens, it's always worth telling the doormen, or the manager, straight away, as they will usually chuck the perpetrator out, but most women are, like you, so shocked and upset that they tend to want to run away and hide.
I know some people on this thread think that the police and/or the club staff will do nothing/are not interested, but that's not usually the case these days. Most are aware that it needs stamping out immediately, and for clubs, reports will have an effect on them next time their license is up for renewal: a reputation as somewhere that goes easy on sexual assault also doesn't help them get customers through the door. And that goes for all sexual assault - whether it's being shoved up against a wall, or having your bum grabbed on the dance floor. It's not on, and it is no longer tolerated. This is not the 1970s.
OP, I'm sending hugs - I'm glad your boyfriend is being lovely. Most men are not like this, and we need to make sure that those who are know that their behaviour is out of order.