Very neatly, satisfyingly done! Thank you, mystery author, for this, with the paired encounters, where each is trying to hide everything he feels, but is able to conceal nothing, though nothing is admitted. That last statement from Severus is such a positive outcome, a promise of moving forward after nearly thirty years. Remus is going to live on that as much as on the memories of the sex between them.
You have a very neat excuse for porn, too, there, in that shared Fidelius (or equivalent) that conceals their true loyalties, and permits them to express their feelings about and responses to each other with a freedom they have never had.