Oh, I simply can't get enough of your possessive!Sirius. He's wonderful. And that he was able to make Remus come from just biting him... And then this:
Sirius brushed his fingers against his own neck, where he could clearly see an angry welt he left on Remus. Remus blushed buttoning his collar to hide the marks. Sirius looked at him intently and mouthed, "Mine."