Anything Goes (Anything Stays)
It started as a game.
Sam had wanted to teach them how to play Shang-Hi rules poker, and to make it more interesting, he suggested they make wagers. As the night wore on and the liquor disappeared more rapidly, Fiona suggested they bet a single kiss upon the losing hand.
When Sam lost, she kissed him - a real kiss, the sort of kiss that would stun a man of lesser experience into catatonia. Sam had given Michael a sideways glance and Michael had reached across the table for him. The poker game was, obviously, quickly forgotten.
Sam would never remember quite how the routine had shaped up after that, but it was one that established itself quickly. Fi was the initiator, the aggressor who never missed an opening and created her own with violence if necessary; Michael was the cool negotiator, the one who accomplished their wildest ideas through any physical means necessary; and Sam, as always, was practical, the realist who got everything done.
It always began with Fi kissing Sam, with Sam touching Michael under the table. Sam would do the unzipping and unbuckling while Michael and Fiona made out ravenously, while they tumbled in a confused tangle of limbs and lips into Michael's bed.
Their routine is no real routine at all. Chaste kisses that turned into open-mouthed plundering, soft caresses into greedy grabs by fingers, licking tongues into bruising, sucking mouths. Fiona wouldn't rest until Sam gave her head; that was his specialty, the thing she craved from him most often. He never imagined when they first met that he'd ever relish going down on Fi, but no one told him that she tasted like spice and musk and something undeniably feminine that made him hard simply to smell it in the air.
He never imagined he would let Fiona go down on him, but then again Michael had never told him that Fi had the sort of throat muscles an opera singer would envy. Sam could pull her up and down his shaft by her hair and she would dig her nails into his thighs but never, ever let up on the merciless suction of her mouth, the teasing lick of her tongue or the dangerous brush of her teeth.
On the other hand, Sam knew what Michael was like in bed before he had experienced it firsthand; controlled but volatile in his passions. Michael liked teasing far less than Sam did; direct stimulation was the way to rouse him. He never failed to give as good as he got.
Sam was the one who liked it when they were tangled together; the power of experiencing Fi's orgasm through Michael's, connecting into his with a supercharge of relief.
Fiona was a show-off; she liked riding Michael while Sam stood by, watching, stroking his cock and waiting for a turn, or getting a quick blowjob. It was her idea to seduce them both with a cup of vanilla frozen yogurt and her even sweeter mouth out on the fire escape one steamy evening. Anyone could have seen them; she wouldn't have cared.
Michael was the peacemaker; he agreed to anything Sam suggested or Fiona wanted to try, if it didn't stretch the bonds of their relationship. Michael didn't have to worry about losing either of them; Sam had a feeling that it'd take a mountain of C4 to pry the three of them apart.
As long as they ended up together at the end of the day, anything went. And that was fine with him.