Well, at least one of them is a responsible adult. *Harrumphs*
On the topic of the Marten/Cosette thing, I think it entirely likely that he would have mentioned it later on, as part of dinner chat or somesuch. Notice that she ambushed him about it immediately after he entered. What was he supposed to do, run into CoD yelling "Dora, guess what! A girl actually asked me out, isn't that crazy!?" But instead she asks obviously loaded questions and he does the logical but dumb for human interaction thing of shutting down until he knows what the questions are loaded with. And she asked that way despite already knowing that his being asked out was an abject failure, so she already had nothing to worry about. So in terms of openness, she failed by asking about the topic that way, and what he did was only a reaction to her deception.