Ursula (male) is a sea wizard who is isolated and feared by the sea known for being evil which he could be. Ariel goes to him accidentally on one of her adventures. So they fall for each other
actually it could be an that he has seen her before and grew to like her
or she goes to him to chase after eric and she fails and they fall for each other after her becoming his slave (which he had done for entertainment"
this just an idea for adoption because I like this pairing but it should have a happy ending