Remus wasn't blaming anyone, not like that. It wasn't because Sirius ever really initiated things - he didn't have to. Just being there, near him, with or without little subtle touches and suggestive words, it all drove Remus crazy. Maybe it was the years of repressed sexuality or the months of not being able to do anything with the one person he wanted. He didn't actually try to find an answer for it because he didn't want to; he kind of liked feeling uncontrollable. Almost.
Oh that grin, he loved it. Especially when it came from those thoughts and actions. But Remus didn't have a good response for that. He toyed with a few answers before going with, "A good one," because it was still truthful. "Surprise me," he added, letting himself relax so that Sirius could more or less take the reigns and show him something good.