What is going on with him?

I met this guy at work who made lots of efforts to talk to me. We started talking online one day when he asked me what I looked for in a guy, how he could get to know me etc.He asked for my number right away and then asked me to meet him up that night for his friend’s birthday, which I did. However, when I arrived he acted very shy and weird so I left. He texted me the rest of the night, innocent but flirty remarks. Since then we have spent time together ( innocent, no dates) and have talked on the phone for hours. He did disclose that he had a out of state girlfriend. My problem is I’m starting to really like him! He texted me after work today and I decided to ask him to hang out. He said no! I know he has a girlfriend but for some reason that hasn’t altered my feelings. What could he intentions be for his behaviors?