What he's actually saying, it seems, is

You can keep the kidney, dear, 'cause I've got another.
But you owe me 1.5 million for the one I gave you so the kids could have a mother.
You threw me over for the neighbor, which leaves my poor heart crushed,
But if I take that kidney back, babe, your whole life will be flushed!"
You don't want to wake up in a bathtub of ice, with a note around your neck.

So let's part friends as soon as you
Write that million-dollar check!"