The "but I don't like... want to hurt you" is rough. Because it's a legitimate concern, she's not just like, a little subby. She's a masochist and wants to be bullied, degraded, and hit. He wants to go to an onsen and have a romantic time, she wants to be his sex slave and be roughed up 24/7. There is actually a sexual mismatch here. It's really interesting because the guy here isn't, like... doing anything wrong. He's positive and willing to learn and wants to make her happy the best he can, but he's doubtful because he literally doesn't want to hurt her and that's what she wants. Like the first chapter is him stopping when she says "no, stop(heart)" and frantically apologizing that he didn't mean to hurt her.
It's complicated because, well... he's the type of person who she can explore these sorts of things safely with. But it also will wear on him. I wonder if she'll ever come to understand this? Maybe that's the point of the new character; not just the potential rival, but to explore that being an actual sadist is like... not a normal fuckin' thing, and that she needs to realize she can't view every interaction through the lens of her fantasies.