What do I do?

Okay, so I have two guy friends - they're both brothers. One of them is the oldest by four minutes, and the other is younger by four minutes.
So the younger one and I always got along the best. He would always smile and compliment me and say what a "great friend" I am. The other one was a little more distant and he wouldn't even call me by my first name until a few weeks after I met him.

Anyway, a couple months later, before school was about to get out (I'm in junior high, seventh grade by the way) the younger brother became really rude and cocky to me. He would be a real jerk and really mean to me. But it's not like he's changed himself - he's still the nice happy-go-lucky person around other kids. It's just...me. He tries to find ways to not talk to me and he insults me now. He used to say I was a great artist and loved my drawings, but now he only criticizes them. But once he started doing that, his brother started being nicer to me. He started paying attention to me more often and talking and supporting me.

Other: The two brothers are fraternal twins. The older one has OCD and a bad case of asthma and the younger one is slightly lactose intolerant and has asthma as well.

I may be over exaggerating because I have a dependent disorder, but I'm really upset about this. I've never said or done anything to the younger twin to make him hate me, so I don't know what's going on. He's still nice to other people. He's...just a jerk to me. Sometimes he and his brother fight too. His brother trying to defend me when he insults me. And I hate it. I hate making them fight just because of me.

Please, I need help to solve this right now.