Oh, I liked this! It's great to see things from Filius' POV, and their relationship really works. I love the little background touches, like Nymphadora's school experiences and Filius making certain Dobby tends the students. And who needs porn when you've got a paragraph like this:
Filius chuckled and Summoned the small pot of oil they kept in the bedside table, then Banished his pants and allowed Severus to help him up into the chair. He could have got there on his own; levitation wasn't such a difficult trick as all that. However, he'd learned early on that Severus found the general physicality of their interaction as gratifying as he did, and he took every chance he got to take advantage of that.