Open Question: My best friend/my big brother/my awesome music partner who ditched all his friends for a chick.?

I call him my bro. He is one of the best beat-boxers I have ever met. I play the violin and he beat-boxes.. so we jam a lot... :) classical vs. hip hop style or classical & hip-hop style. We have always been a team and because we've been through a lot of the same things.. we're close enough that we tell other people we're brothers and sisters. One night, we had a big dinner with our closest friends and we took some silly pictures... which created the most ridiculous problem for my bro. He was dating unofficially with this girl. I know of her and I've had classes with her but we never got to be friends. He called me several days after the dinner and told me that he was no longer "allowed" to be seen with his friends.. and to be exact, his female friends.. to be even more exact: me. He knows it's bull crap and that his girl is just being insecure.. (about my presence with him). I thought he'll get over it or it didn't sound like it was a big deal for him.. but one day I saw him at school and he did the usual friend handshake... and I got so angry because the first thing he said to me was.. "The coast is clear!" I was disappointed. Right now, I'm thinking... My big brother who I have always looked up to... constantly telling me things like "bro/sis before hoes"... has decided to "not be seen" with his friends/me in public so he could keep the girl that he is unofficially dating. Can anyone tell me what's wrong with all this? Because I think everything is wrong right now.