My friend is avoiding me, why?

My friend's a guy. He's been "avoiding" me for a long time. We have mutual friends (who are girls) and he has no problem talking to them. He never makes an initiative towards me, though, and when I start talking to him re responds with like 2 words and looks nervous. When I log in to MSN he immediately puts on the status "Away". He has no problem with for example hugging our other girl friends, but practically fidgets/draws back when I approach. Why is this? I don't drink or smoke, I don't use makeup, I have no fake friends, since I'm very straightforward and stand for justice. My other friends are a bit more shallow, like the type "average partying teens"(not in a that bad way). I'm quite different from them. Is he scared or something?