[In a former life (i.e. before Ianto and blue bands put a stop to his philandering) Aidan would have had plenty of chances with Jack - he's always been very generous with his conquests and very inclusive. And he likes Aidan. If they spent more time together, sparkage could definitely happen.
As it is, though, this is what there is for the moment. For Jack, it's just a kiss with someone he likes but doesn't know that well, prompted by the theme of the day but still warmly given and thoroughly enjoyed, because it's intimate contact and that's one of his very favourite things. He doesn't get as lost in it as Aidan does, but he doesn't back off until Aidan does either, enjoying the moment while it lasts.]