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

I [25M] have been with my girlfriend, C [21F], for over a year. We went through a really rocky patch where this girl who we thought we were both friends with (R [21F]) tried to break us up, encouraged me to cheat on my girlfriend, and talked trash about my girlfriend at every opportunity. Our friend group, of which my brother is a part of, joined in on this. To this day, I still don't know what brought this on- but it probably had something to do with the fact that this girl and I had hooked up once. 

Anyway, to modern day, I stopped hanging out with them because I was sick of how they treated C and how they treated me. Last weekend, my brother invited the whole group to my house to basically day drink, smoke weed, and have a fire. I wasn't really okay with this to begin with and when he brought R, I was very much not okay with it. Especially as the last bit of communication I received from R was that she was going to "turn my brother against me" so that he would hate me as much as she did.

So I texted my brother, telling him I wasn't okay with this and immediately he started attack C- calling her a manipulative bitch, and saying other things I don't even feel comfortable saying on here.

Next weekend my brother and I are supposed to go camping with our parents. One of the main events is watching him cliff dive because a TV network is coming out to film him and a group of cliff divers. 

I am beyond pissed at him, my girlfriend wants nothing to do with him (which I completely understand and support), but what should I do? How do I handle this?
<bot>: My brother did something knowing I wasn't okay with it, I called him out on it. He responded by attacking my girlfriend and saying things I'm very much not okay with.