Okay so from my understanding, it's kind of like the second assumption. Basically when they were younger, they were in love but couldn't actually be together due to him being a human and his lover being a merman. After a few years, the merman got hunted and sold at an auction in which the man had attended and had stumbled upon the corpse or attended in order to outbit other customers so he would be the only one to "enjoy" his past lover's corpse like what he'd had wished for him to do before they parted ways so that was what he did. He bought his lover's corpse, ate him since that was what was wished of him when they were younger, and etc.
Met when they were younger but couldn't be together and broke off with the merman having one last wish (which was exclusively only for the human to eat / savor him since love can also be a metaphor for cannibalism), saw his tail at an auction after a few years, and then kept his promise to the merman
Also like some of the comments underneath, it might be that it isn't the same merman and he's just taking his chances since it seems that he's older now and in order to keep his promise to the merman.
I really didn’t understand, im kind of confused, i assume 1)at first the human guy wanted to try mermaid meat and then he lied about loving the merman so he could taste the mermans flesh but then the human got addicted to it or 2)he actually loved the merman but he got caught so he buys his body and eats the ded merman and then he got addicted or 3)he loved him but he dont know if he is actually bought his loved one so he keeps buying, ( i dont think its 3rd one, they cut the mermaids head off right after they caught but we dont know if they keep the head or not but im assume they keeps the head cause mermaids has pretty face that could sold really well, and why not check the head if the fishers throw the head after they cut off then he will keep eating)
I think the human man is addicted to the meat
*sorry if the grammar is bad*
At first i thought he is buying it because the merman didn’t accept his love and now he is dead so finally he can satisfy his needs hhahaha
Sorry for writing god damn long comment ╥﹏╥