I expected him to refuse, and this is one of the very few times I'm satisfied the protagonist did so.
This 15-year old girl is trembling as she tries to get their first night going. She's 100% forcing herself, and I believe part of her reason seems to be, also to find validation that she's actually attractive due to the painful rejection she suffered. Side note, I like the little bit discussing how otome heroines de-emphasize sexuality and instead put the sexy traits on the antagonist. Otome games are intended to appeal to women, after all. Putting big boobs on the heroine isn't gonna help attract more of that target playerbase.
Kuro has knowledge of the game, but I'll still say it's perceptive of him to realize that his new "wife" was (until very recently) in love with another guy. Or actually still has feelings for, but heartbroken. It's exactly not the right time to bed her. She's not even in love with him, nor is he with her. It's gonna be a casual, loveless act if they go through with it.
No need to rush, it's best to actually do it when she's mentally at the top of her game and actually in love with him, because then she'd be truly enthusiastic about it. Being sexually desired for who you are would be so much hotter than just getting to bang a dead fish on the bed, who's counting spots on the ceiling, enduring the pain and waiting for her first night to be over.
But enough of that, the elephant in the room that needs to be talked about is...
Gray is a girl???