Set up a new e-mail account, forward any important mails and contacts from the old to the new, and then close both the old email and the YouTube account. It's a major hassle, but your account is hopelessly compromised now. The problems from what he could post under your identity far exceeds having to change e-mail addresses now.
On the bright side, this is a chance to cut down on spam for a while until your new account is discovered.
