It was a type of therapy for Jack too, which was a big reason why he'd ended up fucking his way round the dome in that fictional future, to take his mind off being stuck forever. Which... wasn't so different from what had actually come to pass, which was pretty much why he was here today.
He grinned at the joke, but it quickly faded as he studied Kirk thoughtfully. He was just as aware of the tension between them, but he'd also spent the last six months tamping down hard on similar tensions with other people because of the band system and it was a lot easier now than when he'd first got here. Kirk hadn't had that, nor was he as deeply in a relationship as Jack was, and it occurred to him that perhaps, just perhaps, it might make sense to actually address the issue with him before it got out of hand instead of letting it simmer and bubble up until it got out of control.
Especially, you know, given the fact they actually were in a therapy group here.
So he took a breath and said, "Okay, I don't usually spell things out but given how things are I think it might be a good idea here. I know there's this thing between us, and I know the rules have changed, but I don't intend on following through on anything with you, at least for the moment. The thing I've got going, with Ianto and Spike... I don't want to jeopardise that. So for the moment, things are staying the same, and that's my choice, to do it for them, rather than because I've no choice." A beat. "I'm sorry. It's probably not what you want to hear."
It was all unusually awkward for Jack Harkness, considering how easily he would talk about the most graphic parts of sex. Talking about relationships was a damn sight harder!