disconnect gmail when cheked in from another mobile
There are three ways:-


If you have access to the phone (or trust your friend to do it), just delete your Google account from your friend's phone. In the main Settings app, under Accounts, find Google in the list and click on it. Then click your account and click Remove account.
If you've switched your Google account to use app-specific passwords, then you can simply revoke the Gmail password you used to sign in on your friend's phone. Nothing else will be affected.
If you can't wait for your friend, and you're not using app-specific passwords, then just log into your Google account from a web browser and change your password. It will sign out on all the devices and you'll get a prompt asking you to enter the new password.


That said, there's something that doesn't quite add up. It's possible to be signed in and use Gmail from more than one Android device at a time. Signing in on your friend's phone shouldn't make your phone stop working, so it could be a coincidence, which means that signing out on your friend's phone won't fix anything.