Picked a guy over my cousin

So my cousin has been dating this guy for almost a year. I started talking to his cousin, like casually dating, after she introduced us with the intention of actually becoming a couple.

While we were all hanging out, she “accidentally” clicked on his Snapchat (after ordering everyone food from Uber eats on his phone). Instead of getting off the app she decided to look through his messages and he found out. Now they obviously don’t like each other and she made it worse by calling him to argue about it after he was talking to me about the situation on the phone. I can agree that he was being very rude to her by calling her names (And I will say that to him, though I couldn’t actually hear anything ) but she shouldn’t have called him and I told her not too.

She put me on the spot by telling him that I won’t ever speak to him again and that matter of fact, I’m going to block him right now. Girl what? He said that I’m a grown ass woman and that I won’t block him just because she tells me too.. she decided to put the theory to the test and told me while still on ft with him to block him and I just stayed quiet. Nobody could see me or hear me (he was in the room with other people) so they don’t know what I did or didn’t do, but she said “Wow. You’re really going to choose him over me?” And now she’s saying that I betrayed her and that I shouldn’t even be talking to him. She said I made her look stupid and that she would never do that to me.