I'll get back to you. You do have to manually connect to Facebook, so you can just disconnect the account from Facebook. But I'll see if there's a way to change it while connected.
[Update]
Click on your name in the top right corner > click "Settings" > From the settings menu, on the left, click "Sharing" > Under "Connect your accounts" you will see Facebook, and to the right of Facebook, there should be an option that says "Disable AutoShare". Click that and it won't post videos to Facebook automatically.
Something else I discovered is you can now apply for monetization without being a YouTube partner now. Which is pretty cool.