Okay the art is beautiful

Had to read this three times to understand so here's the summary from my understanding.

The mermaid had saved the young ml from drowning and during their encounter they most likely fell in love and the ml promised to come back for the mermaid. The mermaid waited and waited for the ml but when he finally came back it seems the ml didn't remember him but the ml still fell in love with the mermaid.
Once the ml found out he was a mermaid it seems he became self-conscious and obsessed, maybe desperate to keep the mermaid from leaving him and returning to the sea so hence his offer of him going to the city with him far away from the sea (maybe also because his job is in the city)
However (this is probably inspired by the original little mermaid) mermaids who suffer unrequited love will turn into foam and dissappear forever so the mermaid who was starting to dissappear started to think the ml didn't love him which made him want to return to the sea even more because he felt alone in such a big world. This of course angred the ml sending him into a crazed person locking the mermaid up and only using him for pleasure (odd guy..)
Eventually the mermaid ran away to return to the sea on his own, the ml found out about the mermaid running away and chased after him but a deer came outta nowhere causing an accident. Now the accident caused his old/forgotten memories to reappear so now he remembers the mermaid he fell in love with when he was younger and promised to come back to. (This part is speculation) maybe because the ml remembered his love for the mermaid he no longer disappeared and broke free from the curse turning him into a human, or he did something else to become a human to stop the curse from killing him, idk it doesn't really elaborate on that
And they all lived happily ever after