Tosh had been there for him when Jack was…gone. When Jack came back, Ianto felt the split inside himself, of divided feelings, if not loyalties. He'd been involved with Jack for months, loved Jack for a scant few weeks, and never gotten the courage to tell him.
But he'd grown to love Tosh, too.
Jack, ever horny (and with a suspiciously yearning look to his wounded eyes), just smiled that smile full of sex and mancandy and said, "There's such a concept as sharing, you quaint little twenty-first century people." He laid an oh-so-casual hand on his former boyfriend's shoulder and shot a questioning glance at a stunned Tosh.
"That's…um…" Ianto, for once in his life, found himself at a loss for words, never mind witty ones, the mental images playing behind his brain causing his heart to speed up and his cock to harden in his trousers.
Tosh, ever practical, had initially been reluctant, but more because even after working for Torchwood for four years, she was still getting used to thinking not just outside the box, but outside the cardboard, period. To her mind (to Ianto's mind, too) 'stable' and 'threesome' just didn't seem to go together. "I…have always wondered what Jack was like in bed," she admitted with a blush, as she slipped an arm around Ianto's waist, just above Jack's.
Personally, Ianto felt it had the possibility to blow up in their faces when jealousy finally started rearing its ugly head. For someone to whom monogamy was a 'charming, old-fashioned notion' Jack could become remarkably peeved whenever he didn't come first in his lover's thoughts. And Tosh…well, her self-esteem was better than Ianto's own, but Jack had had him first, and her idea of taking a stand involved more passive-aggressive non-action than actual acts.
Sandwiched between his two naked lovers, both of them concentrating on driving any non-sexual thoughts out of his mind (at least when Jack wasn't driving Tosh out of hers)…Ianto considered the rather pleasant possibility that, perhaps, if they worked at it, they could keep jealousy from coming between them.
Jack and Tosh certainly seemed to delight in Ianto coming between them. It just figured that it was only after several hours of energetic sex with the two (living) loves of his life that Ianto realized how much said loves had in common with each other.
In addition to him, anyway.