Why would he lie about having a girlfriend?

I've been talking to a guy for a while now and we get along really well. He told me he had broken up with his girlfriend a while back an didn't have a gf. We finally decided to hang out and when we did it was nice. We hung out at his house watched movies, cuddled, held hands and kissed, he kept telling me how pretty I was. he didn't try anything sexual which I found nice because I felt like he really liked me. The next day he asked if I like him and I said yes and he told me he liked me too. Just recently I found he had a facebook after he told me he didn't and it said he was in a relationship with some girl. when I asked him about it he said that it was old and hadn't changed it. I then went to his myspace and it changed from single to in a relationship. I checked out the girls page and her status says she can't wait to see her bf. Why would he lie? Its not like he just wants sex he's never forced himself on me and we've never slept with each other. He always talks about how he wants to go dancing with me and talks about future dates. Does he really like me? why would he keep lying about having a girlfriend? ohh and apparently they have been dating for like 3 months. I had even told him before that I was looking for a relationship(a bf) and that I don't do hook ups or friends with benefits. and he told me he wasn't like that and he also wanted a relationship but he wanted to "have fun and take things step by step first" I don't know what that means. When I found out he had a girlfriend I told him I had a boyfriend just to see what he did or said( I don't have a bf) he then got kind of upset, I told him I was joking and that I didn't . I asked him what would he do if I did? and he said he'd stop talking to me. I'm confused is that why he's lied about having a girlfriend because he's afraid id stop talking to him?