[Her thoughts are perfectly echoing his own, but the difference is that he doesn't care quite as much about the negative parts of it. He is, for all intents and purpose, available.
It's the fact that he's put Caroline in this position that bugs him more than anything. That isn't what he wanted to bring down on her, because he can't imagine that this won't bother her for awhile.
Which means it probably won't happen again, and he finds himself...unhappy about it.
He laughs, which he hopes it the reaction she was looking for. It's easy to do, since the whole situation calls for either awkwardness or laughter, and the second one feels better.]
You've been thinking about it for awhile, have you?
[He's going to tease her back, because it's the only thing he can think to do without delving into the seriousness and the negative aspects of it all.
Because, like she said before. It was just a kiss. It doesn't mean anything.