Nicely done, Mystery Author! Not a pairing I'd have given credit to, but somehow you've made it work. :-) I love that Greg can read Severus so well - he's not the sharpest knife in the drawer, but he is observant and understands what to do with those observations.
Severus is still very recognizably himself, if a bit subdued since the end of the war and the devastation it has wrought. He's known so little kindness in his life that I'll bet that finding it in the form of Gregory Goyle was something of a surprise, and it must feel really good to discover that someone genuinely wants him.
The Harry/Draco background pairing was very well done, and the 'first four kisses' story is perfectly IC for them both. It's lovely to see the progress in fence-mending since the end of the war - perhaps the feeling we're left with at the end of the books that nothing much has changed isn't quite accurate after all! :-)