100: She
As soon as the words fall from his lips she knows what he is asking. In a very real sense she has been waiting for years for this moment. He'd almost done it before several months ago, but had quickly retreated behind the "atta girl" modifier. Her lips quirk upwards despite herself, but she reins them in, throwing his words from the past back at him in a weak attempt to check his advances.
Of course they are useless and before she is fully aware of what is unfolding she is tasting him. This time there is no tequila, no gum, no puckish prosecutor, no dream to awake from. His hand spans her waist as hers clutches at his chest. His tongue teases at her teeth, seeking entrance and her fist becomes a palm that is pushing him away.
With great effort she divorces herself from him, gaining enough control of her emotions to give the speech she has been perfecting for years. Because for as long as she has known what he would ask she has known what she must reply. This isn't about her protection; it's about his.
She listens as he talks about knowing and while she believes the sincerity of his words she knows things as well. Things like which foot he used to lead with, and the hand that holds his coffee, and his beliefs in fate, and black magic, and lovemaking, and breaking the laws of physics. And for as much as she yearns to feel as he does, she doesn't. She can't.
Yes, she can believe in love in the context he uses it in- he's taught her that much; proved it to her time and again to the point where she knows that is what she feels toward him in this moment. But no persuasive argument in the world could make her know for sure that she can promise him the kind of love he is imploring her for: A love that is not ephemeral. The evidence she has gathered to the present has taught her that it will be. Science teaches her that everything is subject to entropy. That given time it will end and she will be alone. Again.
She would do anything for him she has claimed in the past and so she does, knowing by the set of his jaw and the moisture in his eyes that in doing so she may have just destroyed what is theirs either way.
Meekly, she asks a favor, bracing herself for the inevitable. Everyone leaves eventually. Booth is not everyone and he agrees, but lets her know he will be moving on. She nods. She knows.
And as they leave, they merge, held together by a grief that is uniquely theirs. Except they are no longer "them."
They are she and him.