u/Cautious-Frame-1543

I read this paperback book my freshman year in high school (2018). It was about this kid who went to the fish butcher man with his (dad? Grandfather? I don’t remember which), but he eventually befriended this merman that was in the sea. Apparently some girl the human boy was interested in was the sister of the merman. The crush’s mother was stopping the girl from ever seeing him. The mother shoved him out to sea and had another bay because she taught the merman as “hideous” and thought she’d be shunned for giving birth to him. I remember the book so vividly, but can’t think of the name. Please help!