首先请清除您的逻辑..

First please clear your logic..

1）您正在使用您的脸书要登录到您的网站，那么这意味着如果用户有一个FB帐户，然后登录。
2）如果您是Facebook登录，那么当您从您的网站注销时，您也将从Facebook ...

1) You are using your facebook acount to login to your website, then it means if a user have a F.B account then it login. 2) if you are facebook to login then it is ofcurse that when you logout from your website then you will also from facebook...