SPOILER ALERT
That was such a wonderfully executed Cliche! I adore Slave!Snape and Bottom!Snape but I am aware of how dangerous that particular kink is, as it's very hard to write a submissive Snape. The writing was brilliant! I loved the dialogues!
I loved that Severus tried to escape, knowing he had no chance.
And the sex! The moment where Snape notices his own arousal while being punished was so hot! And then when Snape willingly lets himself be bound in the same position he was in when he was auctioned off! That was so daring and sheer genius!
The whole time I had the feeling that Harry would die, even from the beginning, so I was prepared for the tearful, sad ending! I was overjoyed that you let him live :)