Mixed signals

I'm tottally getting mixed signals from this guy I work with and I don't really know what to do. He has a girlfriend, 5 months, and he say's he's straight, but something about the way he carries himself makes my gaydar fire off like crazy. He texts me all the time, we talk late into the night about nothing at all and he sends me goodmorning texts. I haven't seen him act this way to other people at work. I definitly find him atractive, but last night at a party we both got drunk, I more so than him, and I was flirting with him, pretty heavily. I was also making sure to sit next to him, at one point had my arm resting against his leg, and casually moved it bit by bit as I laughed, drank, etc. It wasnt until my arm was on the inside of his thigh, for a minute, that he asked what my arm was doing. I could feel a bit of something going on while my arm was there, and I was moving my thumb a bit, just before he said it though. He seems to be flirting back, but I don't know if he's just a genuinely nice straight guy or if he is actually gay, and just afraid to come out. He still lives with his parents, so that could be keeping him in the closet.