Oh, I absolutely loved this. I really admire the way you've created such a full (and very readable) story for these two characters, whom I'd never have thought of putting together. You fill them out beautifully: their motivations, wider events and the way these might affect their relationship.
Your Pomona is lovely - I loved her voice, so full of the gardening imagery in a way that was enjoyable without ever feeling forced. I loved how comfortable she was with herself - except, of course, during that time when she shuts Severus out due to guilt.
And Severus. I have to admit that I am not the biggest Snape fan - or rather, I think he is fascinating and a brilliant character but not a very nice man. You showed me a very different side to him here, and one that I can see is hinted at in canon. I loved his interactions with all the staff, not just Pomona. You actually made me feel as if perhaps his life wasn't so terrible and bitter, after all, despite the constant hardships and the awful experiences he must have endured.
I loved the slow development of their relationship, from its awkward beginnings, through sadness and loss, and then finally to utterly vulnerable acceptance of one another.
This is my favourite kind of story: one that makes me see the HP world in a different light. I know I will want to reread it, in order to savour all the details I missed the first time through. Thank you, mystery author, for a great read!