Quicksand indeed, and what a rescue!
Well, like the title, the writing sucked me in immediately! Love it, every bit. This is a fun Snape, powerful and a survivor - like Harry.
I love seeing explorations of this problem they both share, the results of having both survived bitter childhoods through hate as much as any other skill. Both had to don and deal with artificial public personae through much of their teen and adult lives, and realism demands that (unlike the DH Ep) it's going to need addressing.
That they both are "using" this new relationship for self benefit is just another way in which they're both Slytherins -- and Gryffindors, ready to try anything!
I love speculating what Snape's "levy" might be... Certainly, I would be delighted if you ever felt like a follow-up to this. Your Harry and Snape are just so much fun, with that delicious edge of irritating imperfection that you bring out so well.
This is one of those wonderful stories that vividly establishes a rich world simply simmering with promise for further action and exploration. Snarry fen occasionally wonder if "it's done," if "the magic is gone." Stories like this, I think, are conclusive evidence that there is much, much more creativity to come in the Snarry-verse.