"I love you," he says. They just made love so it feels right to be saying it, to be hearing it. But he knows he's loved her for a long time, even though he didn't know it yet. He loves her because she is beautiful, intelligent, and she has a tender side underneath her sarcastic jabs and annoyed sighs. Still, he finds them attractive.
Her head jerks up as she looks up at him, into his eyes, trying to decide if he's being insincere or not. But she knows he would never say anything like this lightly, even though he is a trickster and a comedian. She's been in love with him for a while now, even though she's tried to deny it. She loves him because he is kind, handsome, and he can be serious about the important stuff when he stops cracking jokes. Still, he makes her laugh.
"I—I love you too," she says.
"Even though I'm an idiot?"
"Sometimes because you're an idiot," she laughs.
He loves her laugh. He tells her that.
"I love you," is all she says before she lays her head back down on his chest and closes her eyes, trying to memorize every detail of that moment.
She knows she will describe in detail to her sister, about their first 'I love you'.