Guy friend never talks about his girlfriend to me?

I have a shy guy friend I've gotten closer with over the past year or so. I had a bit of a crush on him till I found out he's involved with someone else, but we have a pretty strong chemistry and he's a nice guy so we are currently friends. We can talk for hours online and have interesting conversations both in person and online. Sometimes I notice him checking me out or staring at my lips or doing the face scan from eyes to lips, but other times if I'm right beside him, he can't make eye contact and keeps fidgeting. I see him everyday at school and we talk about almost everything, BUT he never talks to me about his girlfriend. He's in an on off relationship and will talk to our other friends about spending time with her, but with me, he's vague and barely ever mentions her. For instance, they went out one weekend and he told our other friends when I wasn't there where they went and even that the restaurant messed up their order and stuff, but to me, he said he ran errands and 'some other things'. When we're chatting and he needs to go, he doesn't tell me he's going out with her but it's obvious. And once I was upset and he asked a mutual friend if she knew why, and he was saying sometimes he doesn't reply right away when we chat because his girl is present. But he's never told me this, just that he has to get going with his studying. Why does he behave like this with me? Does he not trust me enough to just be honest? It's starting to really bother me.
Guy friend never talks about his girlfriend to me?
Post Opinion