Search Results: flirts with me even though has a girlfriend

I think a coworker was flirting with me. I caught him checking me out a few times and before Christmas he strikes up a conversation with me and tried to extend it during the entire shift. He also kept asking me questions about my plans for the night, weekend, my living situation and offered several times that day to drive me home since we live in the same neighborhood. I had a feeling he was flirting with me because he seemed genuinely curious and always agreed with everything I said as if he wanted me to approve of him.

About 4 weeks later he came into my office (wearing pretty much cologne) even though there were plenty of empty rooms available so I figured he might like me a bit. But that day he was very busy and very disinterested in the conversation as if he tried to make the point that I’m not his type. Later he disclosed that his girlfriend was about to move into his apartment.

Now my questions are:

did he actually flirt the first time or was he just trying to be nice to a new acquaintance?

And if he did, why would he try to suck up to me if he already has a relationship and then pull back and act super disinterested in me?