Looking for a BL

I can't remember the title, but if i remember correctly, this story is completed. I want to reread it again, and the story is about two college dudes. The ML sleeps with the MC for fun (or smth), and this ML has a big secret. He turns out to be a prince, and he's a merman. But since he's been living with humans for long now, his injuries are getting worse (like there's crack thingy on his body) but he refused to go back to the sea because he eventually fall in love to the mc. This is all i could remember. Please help meee