I requested this from NetGalley because the book description really reminded me of The Little Mermaid (the Disney version). As I read this it is clear that the main character, Aliya, is a bit different from Ariel. Aliya is able to feel the emotions of this human man (I think mermaids in this book have abilities to feel emotions) and so she is in the water next to his boat purposely feeling his emotions as he is getting it on with another woman and it clearly sounds like she has done this before. If that isn't creepy, I don't know what is.
(eta: it turns out the guy isn't a prince so I edited my reading update. Also Aliya isn't the only magical creature in this book that is obsessed with watching humans get it on.)