The kind of conversation the dude should have with Asano. If she wants a long, perhaps permanent relationship with him, this is something she needs to know. Of course he could change and his distrust in relationships might never affect them, not even after 30 years into marriage, but maybe it would. It's not exactly a small thing.
It's understandable why he never had this kind of conversation with her. After all, he thought it's all over in three months and the whole thing only exists to make the mentally unstable mother feel better. In that scenario, the less Asano knows, the better. He's not a scumbag, so from his own point of view, he can't enter a permanent relationship hiding such a weakness in his character (should you call it that).