remove my account from someone else's xbone

There is no way to remove an account without being at the physical xbox.

If you are worried about him getting on your account on his xbox you can change your password for your account and next time he tries to sign in it will ask for the new password and if he doesn't know it hes not going to be able to sign in and would then
not be able to do anything on your account.

Change your password and also make sure your xbox that you own has the xbox home set to that xbox as well

You should go and remove the account personally then when its removed change your password and this will stop your cousin inputting your details and using your account.

Even if you gameshare with your cousin you can keep your account on their console as the home account and if you choose a new password your cousin can’t access your account and log you out but can still get the benefits of your gold subscription and any
digital content you own without login into your account and logging you out.

Also you could attach a passcode onto your account when logged in on your account on your cousins console then they cant access the account but will allow you to sign in when nedded if you play on that console when you visit without having to keep putting
your Microsoft password in to get into your account on their console.

Head over to https://account.microsoft.com/devices/ and log into your account. Then you can select the particular device that you don't want your account on, and rekove that device.

You have to reorganize the Xbox.