Scott meets Jean's hunger and intensity, but a couple of factors are keeping his physical response - level of arousal - just a little tamped down. The simplest of those reasons is just that one of them has been dosed with an aphrodisiac and the other one hasn't. The rest is more complicated and -

really doesn't matter to him at all because she's leaned against him, kissing him and even if he is not wholly engaged, he's engaged enough and he's never wanted anything as much as he wants that kiss and that moment.

Logan stopping in the alley pings off Scott's sense of movement a split-second before Logan speaks. He turns his head that direction and pushes Jean back and away from him. It's the very start 'ready to blast something to hell' type move, but it doesn't go further than that.

It doesn't go further than that because it's Logan.

He just settles back against the wall, puts both his hands flat against the wall and watches. He's wary, yeah, a little defensive and irritated at being interrupted and not sure of what his own response might be.

He's also just... interested in seeing what Logan's going to do.