I absolutely loved this! Sirius/Ron is one of my guiltiest rarepair pleasures, and I've rarely seen it handled as well as this.
I adored Ron here, all provocative looks and momentary want, and him giving Sirius the short shrift after is *extremely* Ron.
And Sirius himself was so gorgeous - I loved the way you portrayed him, a sort of boy's mind in a man's body, having forgotten (and having had stolen) most of the time in between. Never grown up, and never really changing, and very Sirius in his instinct-driven, petulant ways. His impatient 'seduction' of Ron was wonderful. I also enjoyed the Sirius/Regulus backstory, but loved the Ron/Sirius (the new R/S? Just wishful thinking) to bits.