Girl if you were stuck in a chamber and was tortured nonstop all day everyday, then someone handsome came and sliced off the necks of your abusers and opened the door to your salvation...you’d develop affection.
Not only is she a precious existence in that sense but the blood is also making the both of them lusty and turned on.
You pay too much attention to the whole blood thing bc I get that the author shoves it in everyone’s face cuz that’s the story, but you didn’t notice how he was noticing her personality and was actually really fond of it.
The fact that she is so bold, fearless, and expresses herself how she wants is attractive to him. Otherwise her head would have been chopped off and all her blood would have been drained for his consumption the moment she bashed his head, and if not in that moment how she just opened the blinds. He was observing her actions and is super fond of it. Not to mention how despite calling him monster and blushing furiously oh and almost dying three nights ago, she forgets all about it and sincerely offers her help just because she thought about him being in some kind of pain.
So it’s not “just because of her blood”
And im sure everything he’s going to find out about her old life as an outcast and the strength she had to ask to get revenge with her own hands...yea...he’s gonna be head over heels.
I mean I guess but if he killed her for her blood it’s kinda risky. He's practically slaughtering his only chance. How long would that last? She almost died last time and it lasted 3 days. You keep a chicken alive for it’s eggs, right? Same concept. You may kill it for the abundance of meat once, but that’s it. Then it’s gone and you’re hungry again.
As for her personality I guess. I mean, he’s entertained? But again, if she was anyone else she’d be dead easy. She has worth so she is alive. I don’t think he’d value her less just because her personality is less quirky. And she helps because that’s who she is. Besides, if she doesn’t, she’s dead anyways. That’s the reality of the situation.
I feel like right now he is noticing her and feelings are developing, but there’s nothing wholesome there. So his sudden affection is more of the influence of blood, like you said the lust, rather that placed from the heart.

I like their relationship but I suddenly feel weird he's so affectionate just because of her blood. Like there’s no genuine build up in feelings. But they’re also technically married so it’s better than him being nonchalant I suppose.