Hi everyone,
I saw this drama a long time ago but I forgot the name and I'm having trouble remembering the story so I'll do my best.
The story is based on the relationship between a girl and a boy. His friends bet him to seduce the girl and he succeeds. But we quickly see that he really falls in love with her and he does not admit to her that it was a bet at the beginning.
She ends up learning it but after that, I don't remember too much about what happened.
I remember that the end of the series ends on this: she understands that the boy is in danger because another man has come to attack him at his home.
She runs to his house and a violent fight breaks out during which at one point the boy intervenes to protect her. He thus takes a violent blow instead of the girl and faints.
Then, in the end, the two characters leave each other and we see them again 5 years later. They have both grown and changed and they meet again almost by chance. In fact, the boy found the girl because I think he bought a house that she had the job of selling.

Thank you in advance for your help !!!

This sounds like Tempted/Great Seducer starring Joy and Woo Do-hwan.

Seeing you posted this in the Korean section I’m thinking it was an Korean title? The story sounds familiar, Tempted came to mind but I don’t think it’s the title you’re looking for. These are not Korean titles but they do have a similar story…

this is a Filipino movie https://mydramalist.com/27670-just-the-way-you-are

this is a Taiwanese drama https://mydramalist.com/81-autumns-concerto

i have seen Autumn's concerto and the story seems the same 

Yes, it was "Tempted" !!
THANK YOU SO MUCH!