Or, if the relationship is offering something that the other wants.
Generally, I avoid romances where one person has all the say. I'm not terribly fond of the "civilizing" or corrective relationship.
However, I tolerate a great many frenemy relationships if I believe that the relationship is filling needs for both parties.
Selfish Mr. Mermaid is a great example. The male mermaid ("mermaid" is used as a general term for "merperson") moves into the protagonist's apartment, specifically his bathtub. And stays. He argues that he was kicked out of the undersea realm but he appears to mostly just be irritated by people's demands at home, especially since he grouchily takes his lover home for various state shindigs.
The protagonist, however, doesn't come across as cowed so much as relieved. He hates his job, where he is bullied. The kind of bullying offered him at home is tonally different. He is rebuked, cossetted, commanded, indulged, and basically looked after. When the merman does yell, he comes across as mostly confused--"Why are you crying?!"--a far more confidant Rochester--rather than domineering or pushy.
Part of why the manga works, of course, is that merpeople are already unpredictable chaotic figures who are, nevertheless, very, very cool. Of course, the protagonist isn't going to kick the guy out!
However, the manga 2-volume series succeeds because the relationship actually seems to work. The protagonist doesn't wilt but thrives. He is very happy in the relationship.
