[Stopping would be the smart thing to do. It would be the right thing to do, or at least what he's always thought of as the right thing. Don't get involved. But he already is, isn't he? And he doesn't want to stop here, he trusts that it won't get too out of hand and honestly, they've been playing it so safe.
The inner struggle translates all too easily into his expression, even more so when he tips his head forward to rest against her shoulder with a frustrated sigh. He doesn't want to, but they should. Probably.]