He hasn't admitted to himself yet that he isn't sure he'll ever truly be ready to kill her. Lua is so looking forward to it, and he doesn't want to disappoint her, and he does want to do it, he really does, but the longer he waits, the more unsure he is that the time will ever be right. He's put so many grandiose goals in place because he wants to postpone it as long as he can, and he wonders where everything went so wrong that he actually has second thoughts about it.
More than anything, he wants to see her face when she goes, he wants to see that beautiful life leave her eyes while she smiles up at him like he's her whole world, and in her final moments, he knows he will be. He wants that so damn much, but it's what comes after that he isn't so sure about it. Several times, he's brought her so close that he's afraid he's gone too far, too soon, and then she comes back to him and it's the greatest relief he has ever felt. He knows that when it's done for real, she won't come back from it, and he doesn't think there will be a moment after that that he is not waiting for her anyway.
She sometimes asks him, and always he tells her, "Someday, you just gotta wait for it," but that someday is feeling more and more distant. He loves her so much that he knows he owes her this, his greatest gift to her, but he's afraid he's going to end up failing her. How can he want something so badly, and dread it at the same time?
He slips his hands into hers, pulling her up against him, and she smiles up at him like he's her whole world, with that life in her eyes that he wants to be the one to put out, but not just yet. No, not yet.