Michael has to go back to being quiet for a minute after Lee replies; he's worried that if he says too many things at once, he'll lose control of himself. All of his focus is on keeping his shit together, both because it's necessary and because he'd rather focus on that than on the whys and hows.
He's thankful to be back in Lee's arms, since the more firmly she holds him, the calmer he can stay. He thinks about her breath in his hair and the repetitive movements of her living body. He thinks about how he has a place to sleep, next to her.
He has all that, and he's still wretched and crying. What does he need?
“Just stay,” he says, because maybe nothing can make it better, but it could still get worse.