I think the man I'm seeing has a girlfriend?!?

Hi, I've been seeing this man for nearly 4 months now. The problem is that we met in a club and exchanged blackberry pins so always talk on that. I don't actually have his number. When i asked him for it, he said no and said it was funny to wind me up. He also won't add me on facebook and again uses the same excuse. I know this may sound quite childish as facebook is only a social network, but it's really getting to me! I've also heard through some people that he hangs out with this girl a lot and when I asked him about her he said she was his ex girlfriend and they're still really close. I don't know what to think. I really want to believe him as really like him but all the signs are pointing to him having a girlfriend? He also goes really hot and cold with me, sometimes i see him lots and talk all the time and others he'll totally ignore me for days. Please help!