I was Possessed by My Favorite Childhood Friend

I possessed a web novel. And not just anyone—I became the childhood friend of my favorite character.
Who’s my favorite? Of course, the female lead!
Since I got lucky and became her childhood friend, I thought I could forget the original story and just live happily as a successful fangirl.
But the world doesn’t leave me alone.
If things are like this, then I have no choice. To protect my favorite, I’ll even do dirty deeds if I must.
But then, out of nowhere, she says something strange to me—
“Riela, please become my family.”
“…What?”
“I know my brother isn’t good enough compared to you. But I want you to be my sister-in-law. That’s my wish.”
Wait—me, marrying your real brother? Isn’t that going too far?
And besides, isn’t a proposal supposed to come from him?!
***
“Don’t worry about anything else. Just think about yourself. What you want, what you desire. I’ll always stay by your side.”
My life’s goal was to make my favorite character happy.
“Daniel… why are you going this far?”
“Because I like you.”
I thought if she was happy, then I’d be happy too.
“But it’s because I love you.”
…Is this really okay?