I'm going to venture to guess (as a female myself) that you like this guy a lot more than you either think or admit. (one or the other)
The fact is women want men to be mildly into what they're into. If you are lucky to find a guy who is into what you're into then you count your blessings. For example, if I stumble upon someone who is equally geeky with me about technology and who will not only put up with but join in my camera fun on vacations and just in general terms around town then I've hit the jackpot as far as mutual interests go. However, you have to know that there will be some things that you're into that he simply will never understand.
I am a hugely sensitive person about certain things and things expressed through IMs are not off limits. His response doesn't come off as callus, only that he simply doesn't understand. Did you attempt to help him understand and if so, why are you? You said the two of you just drifted so unless you care for him more than you think / admit then I'd have to say you're just wasting your time. So what? He doesn't care about your dancing. If he is a friend he would care that you care, but maybe he hasn't hit that maturity level just yet. Perhaps he has and this is him.
I have but one sage piece of advice to offer you about men. "You can't teach a bull to dance, but if you do try, you'll wind up with a lot of broken dishes."
Don't give up on him just yet, friends are far too precious to just give up on over a misunderstanding and under the direction of a pack of strangers on the interwebz. Help him understand and in his own time ... if you two really are friends, he'll make whatever effort he can afford necessary to try and support you.