Why does my guy friend act like this if he has a girlfriend? (sorry for taking so long!!)?

I think he likes you and doesn't like his girlfriend. He's probably confused. You as a good friend should talk to him, I know you like him too. You can also get a facebook account if you don't have one. You just have to be careful, but there's nothing wrong with facebook. All you have to do is accept people that you know ONLY. Do not accept strangers. But yeah, talk to your friend and see what is going on. You are a lot more open than him anyways, so try to get him to open himself more. If they teased you both it is probably more because of him, so yeah you can stand up for him too if you want.