Your physical appearance seems fine, otherwise you wouldn't be getting internet dates in the first place. Also it wouldn't be an aspect of you which is overly evident on the first few dates (like body odour). Hence I'm placing my bet that it's on your personality (not to be too harsh). That's the only reasonable explanation why girls stick around with you initially, but then break it off as they get to know you better. But there's nothing wrong with your personality, there's just something wrong with your dating method. Lots of internet dates/blind dates/speed dates don't work because of personality clashes. Instead, you should date girls within your social circle or get to know them better before asking them asking them out.

Just trying to put a girl's perspective...which is kind of lacking in this thread.