Yes. If the interloper has your username and password information, they can easily log back in. It's for this reason, you should also change your password and enable Facebook's Two-Factor Authentication feature. Do keep in mind that 2FA will not keep someone out of your account if they've saved the browser or device they used to sign in. You'll need to change your password and verify that all of your account information is up-to-date and accurate before your account is secure. We have an article here that will help you set up Two-Factor Authentication.