Yeah I thought this in the previous semi-chapter too, if he got rekt by some other woman and became really cold. This also ties in with some comment in the first semi-chapter which jokes about him originally being tsun-tsun to begin with (or at least that's how I interpreted the comment).I think the Marquis has some trauma with women in the past, and because he lost his memory and he also forgot his trauma, he become a man who can fall in love easily. Basically saying, he become naive.