I find this fine because ML doesn't sexualize FL and is pretty pure and innocent (maiden-ish some more) about the whole relationship thing (and even got embarrassed and shocked by FL's words about the "making an heir" part), so I guess a bride/wife to him is like "Finally I get to have a (human) family that loves me and cherish me that is not Rave" in his seemingly naive mind. He treated her with enough respect and care too. Pedo is after specified sexual feelings toward minors after all, and he doesn't exhibit that "interest" in his behaviours and actions (so far). They are only at engagement stage now, which is pretty common to even have people engaged before they were kids or even born in ancient societies with nobility system, they are also keeping everything pretty pure and innocent in agreement. The Prince on the other hand though, which is canonically incestuous...... But then royalty siblings/cousins in sexual relationships aren't unheard of in medieval/ancient societies too, Game of Throne also has had that depicted, so there's that. In context, it's not a really deal-breaking conceptual display for the story to be so "controversial yet brave".
Anyway, it's kinda funny how FL is thrown into the whole confusing messes right after she travelled back in time lmao. Usually, time-travelling fantasy would give the MC some time like a few days/months before the turning point event to reorganize thoughts and stuff. Rave is pretty cute, sassy and witty too, especially "I heard, I heard. About what a mess both you and the little miss are" with a casually deadpan face.