Sunoo had gotten into an accident, causing him to lose his memories, including the memories of you

the only people he remembered were is parents and his 'girlfriend' who Isa claimed to be but in reality she was just someone obsessed with Sunoo

you loved Sunoo a lot and you couldn't bare seeing him that way, you wanted to tell him all your moments together in hopes of his memory coming back but it was no use

"I'm sorry.. I don't know who you are"

Credit: rikiiverse