(Doesn't he, though? Shouldn't he? It feels like he should be but... he can try not to be? He doesn't want to be worried, and if she says so...)
"Okay, sure," he says, and goes back to being snuggled in her arms, doing his best not to think about anything.
(But what is she thinking about, though? Does she think he's not ready for this and is going to change her mind at the last minute? Does she think she's not ready for it? What did he do wrong that made her have these things happening? That is, if his worries are real. But are they? She doesn't feel like she's second guessing anything maybe (how would he even know) but she could be?)
No, no worrying. He should stop and be comfortable where he is and think of the fun things that are going to happen soon. (There are such fun things going to happen soon. As long as they do happen that is because if Rosy has changed her mind... fuck. Fuck.) He goes back to trying not to worry about it.