Chiba is straight up trying to live out his isekai harem power fantasy life and won't listen to anything Haru says that tells him otherwise. He doesn't want to get the priestess until he locks down Haru as his sex slave maid girl (lmao yikes) like there's absolutely no loyalty in him other than the one he has to his fantasy.
I think Haru genuinely likes Sumo and that + her desire for independence is what keeps her from pursuing him as a love interest/marriage partner. Like she's not willing to depend on one man for her livelihood, regardless of the man himself, but also I think she'd rather Sumo find a nice girl who *wants* to be his wife rather than use him to get out of sex work (which is something that she's more than willing to live with).
What a lot of people don't seem to get is that Haru considers sex work to just be work. Granted, in this universe it's very dangerous work in an even more misogynistic society than the one she came from, but it's work that she's skilled at. And it's satisfying for her in its on way (tho not usually /sexually/ satisfying), though again... I feel like she'd be happier if her work/customers were safer and society wasn't set up to bone her, but getting out of the business isn't something that she thinks of as her first step towards a happier life, or she'd be actively pursuing it. Haru isn't a wilting flower too afraid to work for what she wants.
Side note: I don't think this universe has untreatable STIs (correct me if I'm wrong tho lol) and they definitely have contraceptives. Haru's true danger is being raped and/or murdered, which is the same thing that happens to a lot of sex workers — tho the same can be said for all women.