In his manic intoxication, Fabian somehow found enough presence of mind to need to reciprocate. He could no longer concentrate enough to handle two tasks at once, so he chose just the fingers that were still inside Sirius' body. His now free hand went to Sirius' hip, holding onto it as his orgasm-heated mouth dropped against the man's nipple.
He sucked, bit and licked at it, breathless as he smoothly worked Sirius' body for all it was worth, and Sirius Black's body was worth a whole fuck of a lot.