It's hard to say. I wouldn't quickly say yes just yet because he could see you as a really good friend. Don't make the same mistake I did on that.
If you really want to know, then see how he acts around you. Notice how he treats you and how close he is when he's near you. Take note on his posture, how he looks at you, and any sign of flirting. If you don't see any, then probably don't pursue him. If he does, then this could be a sign. But I wouldn't act on it too quickly. Look for more signs or just ask him straight up.
With his girlfriend being not supportive, this could boost things. But don't trust too much on this. I'm just saying that it could help.
Relationships is tricky waters to tread on. Too quickly or too slowly, you may drown. Just from reading your question, this is all I can gather from it. I hope there was something that helped.