To be fair, Jack hasn't quite been sure they're really there yet either, and he really wasn't intending to push things, but he's such a creature of instinct that he just went with his gut feeling at that instant. He's totally prepared for Ianto to reject him, and so the wave of emotion that washes through him when Ianto gives him that funny little smile and leans in again is unexpectedly fierce. Things have felt slightly off with Ianto ever since he and Spike arrived (however much Jack has been playing it cool and easy) and it's such a relief to feel able to connect like this, the way they've always communicated best.

So he meets the kiss with relief, trying to keep too much neediness out of it but definitely wanting. His hands stroke into Ianto's short hair as he drowns his senses in the feel and scent and taste of Ianto once again.