This is the page monday mentioned the story I think
http://www.mangago.me/read-manga/heaven_hell_roman_company/uu/heaven_hell_roman_company-chapter-46/15/
And this is the whole Greek mythology story if anyone wanted to read it. (It's sad af tho but kinda a happy ending?)
https://www.greeka.com/greece-myths/orpheus-eurydice.htm
If anyone is wondering what Monday was talking about when he mentioned the names Orpheus and Eurydice it's based off of a Greek mythology story about "not looking back" and I'm guessing that's why those things happened to them and they lost their memories. But in the Greek story Eurydice dies. I hope Monday doesn't die tho