It's rare in Snarry fics I've read to have the opportunity for Snape to observe and be jealous of Harry with a girlfriend. It's something I enjoyed immensely. I have such a thing for jealous!Snape.
Snape thinking of what he could offer Harry is such a Slytherin way of thinking. It was pleasing to see what Harry could get out of sex (and maybe more?) with Snape and likewise.