What's up with this guy?

There is this guy, Nate, in my cl who is pretty popular. He is friends with this girl named Brianna who I have never liked. I am in 10th grade, and ever since Kindergarten, Brianna and I have went at it. When I say that, I mean we have times where we insult each other and argue until a teacher tells us to stop. Brianna used to be the joke of the school, but ever since she egged someone's house, she gotten really popular. She got even more popular when she slept with a guy who used to go to my school, but dropped out, on the first date. She is still the biggest b**** in the school, in my opinion anyway. My friend Joe kept throwing pens in my face, so I threw his ignment notepad in his. Of course, the teacher didn't catch Joe but he caught me. And he was just like hey! pick that up and stop it! And so I did and Brianna was like yeah stop it. And then she muttered to her friends, Nate, Rem, and Christina, "That's what we get for sitting next to them." I'm pretty quiet, not including the fact that I've gone at it with Brianna in the past. I actually hadn't gone at it with her since 8th grade, and that was when me, Christina, and Brianna went to a different school then Joe, Nate, and Rem. I am really sick and tired of Brianna putting other people down to make herself feel better about her lame life, so I was like why don't you mind your own business? Or is that too hard for a skank like you? I could tell she was really suprised that someone stood up to her, because ever since she's been popular, she just picks on people and they don't do anything about it. Nate was really surprised too and looked back for a couple seconds but then him, Brianna, Christina, and Rem went back to their conversation. Ever since then, Nate has been acting different. Like, after I went to the bathroom, I came back to the cl and the door was locked. Nate opened it but stood in the doorway and asked for a pword. I was like can you just let me in please? and he was like yeah, I'm only joking. And then today, we were watching a movie and when he came back from the bathroom, he was going to his seat which is in front of mine, and then stood in front of my desk and blocked the view. And then he says, Oh sorry. didn't see you there. And I know he knew I was there, because he had already turned around earlier and told me that he missed the answer to question 2 on the movie sheet, and wanted to know if I had it. And after he said he didn't see me there he asked me if I thought he was funny. I was like sorry, but it wasn't. Do you think he is actually mad about what I said to Brianna? Rem and Christina aren't; they haven't acted any different then normal. Is Nate mad or is he trying to be friendly? He never talked to me before I told Brianna off. I know this question shouldn't be in friends because I'm not friends with him, but I don't know where else to put it.