"Because I can't let go of you, either, you idiot!" If Eiji's going to turn the words around, then giving him his back only seems fitting. There's more he could say about why, but it's either things Eiji should already understand or things he still doesn't want to admit.

"You said it before, didn't you? We're stuck with each other." Except that now instead of threatening to kill each other, they're both desperately trying to keep the other one alive. "Get used to it."