Ahhh, the fantastic art of lonerism has its side effects and drawbacks as well. I can definitely relate to your situation probably because I've always been a loner myself. Even when I was in elementary school I remember willfully distancing myself from my peers, not because I disliked them, not because they disliked me, but simply because I enjoyed being off my own thoughts rather then engage in the general notion interaction. But as Nietzsche has said (paraphrased), a man who stands alone is either a god or a beast. I know that truly I was not either, and so the effects of isolation in combination with society's insistence that loners are dangerous and weird individuals have inevitably made me think of myself as somewhat of an extraterrestrial among men.

As for your situation, perhaps if you really don't want to go you could just say you're feeling sick or something like that. Or maybe show up very briefly to greet everyone, but then announce your hectic schedule and leave right after.

Take care,
~Monsieur