Is it normal for me to have a crush on someone i only know over skype?

Around a year and a half ago, my friend introduced me to a guy on Skype. We talk quite often, and we're pretty supportive of each other. When one of us is depressed, the other knows how to cheer them up. We live in the same country, we have similar interests, and I'm pretty certain we both enjoy each other's company. But, he has a girlfriend. I would try to get over him, but he's the guy I usually talk to for advice or if I'm upset, and I'm not sure who else could replace him. I'm not sure if I'm just being silly, or if its something else. He told me that he doesn't tell his girlfriend about his depression issues, but he's told me. I don't know! Is this normal, and what should I do?