"For both our sake" or "for both our sakes"

Should sake be pluralized in this usage?

For both our sake, I'm going to leave now.

For both our sakes, I'm going to leave now.

Yes, the word sake can be pluralised. For both our sakes sounds a lot more natural than for both our sake. You can also say for all our sakes.

Of just 53 hits in Google Books for "for both our sake", some are actually "for both our sake's", whereas "for both our sakes" gets 84,000 hits. Forget logical analysis - just go with the majority!

But... note that (as @Peter Shor says) in OP's example it's the word both that puts the kibosh on the singular. Without it, the modern trend is increasingly to say for our sake

("for our sakes" was actually the more common form a century or two ago, if you want to look)

It doesn't appear that "for both our sake" (with singular sake) is ever used. (Ngram for both our sakes vs. for both our sake; corpus English; 1800-2008.) I agree with FumbleFingers -- go with the majority.

You can't say "both our singular noun". For example, while "both our houses" is correct, it necessarily refers to two houses. If you want it to refer to one house, you either have to leave out the both and say "our house" or say "the house of both of us".

So the choices you have are:

for the sake of both of us,
for our sake,
for our sakes,
for both our sakes.

I would say that logically it should be "for both our sakes" because "sake" is plural in this sentence. However, maybe grammatical logic is sometimes illogical as in "for our family's sake" because there is only one family although there are obviously several people in a family.... However, having written this I am unsure about the answer...