School

So, I'm a little confused. 

There's a boy. And he like..it's handsome and all the thing. He is very popular in my school, like VERY popular. His name is Alex.

And I was thinking; If he's popular, it's because, besides being handsome, he's also nice! Yeah, so I got the wrong idea. 

The other day I tried to talk with him, cuz I just want to be her friend, besides, I know he has a girlfriend and I respect that. The thing is, When I approached, he was with his girlfriend and a couple of friends. I thought there wouldn't be a problem; his friends and his girlfriend seemed like nice people. Basically, I stood in front of him and greeted him. I said 

"Hello! How are things?" Trying to look cool. But when I turned around to greet her friends (along with his girlfriend) she was looking at me like she wanted to.. uh..k*ll me. And he literally stood in front of Alex and grabbed his arm. Then, Alex stood there uncomfortable and didn't even greet me back. I don't know if I was wrong, or he or she was. Now the girl is saying I'm a boyfriend stealer..what should I do? help pls