I don't really know why, and I haven't told my old man. He'd tear me a new one.
He's been sucking on people. Mostly Adam. My half-brother. But I doubt it's been just him. Of course, it's just recently that blood started disappearing from the hospital, and in all honesty, I don't think it's Damon. He's been here a lot longer than that.
Either way, he's not on a cattle diet, and the last time I let a vampire live, that was the deal. No human blood.