Brilliantly written story. I generally prefer Harry to make the first move, but it is totally convincing for this Severus to initiate their relationship. I've always loved the mixture of succumbing to temptation yet still obtaining a strong sense of honor in his character.
"To forestall further attempts at conversation from that direction, Snape helped himself to some strawberry yogurt, and filled his mouth to make replying impossible." This must be the most endearing action from Severus I've ever read!!!