This might sound a bit odd, but... are you SURE they were being genuinely mean, in a malicious way?
Something I've noticed about *lots* of people on the spectrum is that many cannot tell the difference between banter, and insults. I'm not entirely sure the word "banter" is correct, but that's the word I know for that sort of behavior. This is something that absolutely needs to be considered with a situation like this, however it seems to be extremely difficult for many on the spectrum to grasp the idea and spot it, even if it is explained to them (and I have indeed tried to do exactly that a few times).
Before instigating any confrontation, it's important to take the time to try to REALLY understand. NT behavior can be very confusing for many of us, and it's super easy to misconstrue basically all of it. It's also important though to confront your own thoughts on the matter. It's easy to get into the mindset of "Of COURSE I'm correct on this" and that habit is hard to break out of.
Discussing these things with your friends is a good idea, but dont make it into an angry conversation. Talk to them, one-on-one, and specifically point out that you want to have a serious conversation... no joking around. Most people, NTs or otherwise, understand what that really means. Ask them directly: WHY do they say the things they do? What do they REALLY mean? Explain to them your own thoughts on the manner (in a calm way) and make sure they understand the difficulties you face, so they can get an idea of where you're coming from on this.
If it turns out that they genuinely dont like this girlfriend of yours, ask why that is. Sometimes, a given situation isnt as simple as it seems. Perhaps there is something that, with a bit of work, can be fixed somehow. Consider also that these friends of yours may have other things going on that can affect their mood and behavior. Someone going through depression and stress, for instance, is much more likely to lash out at random for no good reason, and that's not easy to deal with, but it absolutely happens.
Again though... dont get angry about things while talking to them about it. Remain calm and rational during the whole thing. And accept the possibility that it may not end positively... but dont ASSUME that it will end in any specific way. You cant know until you go through with it.
Good luck to ya.