I have over 300 HP slash recs - almost all of which feature Snape - and only five of them are Snape/Black. As soon as the reveals take place and I see who wrote this really excellent story, that number will be increased to six.
Truly fine work. Good pacing, and very believable characterizations (plus extremely hot sex scenes, which - for somebody like me who's started skipping over most sex scenes because they're all beginning to seem "by the numbers" - that's saying something *g*). Well done, mystery author!