I don't know if it's a Manga or Webtoon but I can't seem to remember the name of it.
I apologize first because it will not be in order.
The main character is a adult male that wears a teddy bear costume and a girl student.
They met in a tunnel(or something) that the girl named when she was very little but she doesn't remember and the guy remembers. The guy comforts her when she is sad and and crying.
He gave an umbrella to her when she was very little.
The main girl has a friend who has a alcoholic father who beats her up at night and she likes a guy and dates him but afraid that he will not like her because of her father.... Etc.
I'm sorry but this is all I remember.

I think this is Sikeum Saekeum

Yess! This it it Thank You soo much!!!!