How do I put the Xbox account only in a different email address ?

they cannot be separated, as the xbox account is the microsoft account and you own the microsoft account then the xbox account is also yours and not his.

he will have to create a new account and start over.

I'm sending you some YouTube links where you can make the configuration, watch them until the end so you can understand exactly how to carry out the process.

https://www.youtube.com/watch?v=YPyUA6qSGmU

https://www.youtube.com/watch?v=tdkg1LrLeHE

This is a non-Microsoft website. The page appears to be providing accurate, safe information. Watch out for ads on the site that may advertise products frequently classified as a PUP (Potentially Unwanted Products). Thoroughly research any product advertised on the site before you decide to download and install it.'

I'm sending you some YouTube links where you can make the configuration, watch them until the end so you can understand exactly how to carry out the process. https://www.youtube.com/watch?v=YPyUA6qSGmU

https://www.youtube.com/watch?v=tdkg1LrLeHE

This is a non-Microsoft website. The page appears to be providing accurate, safe information. Watch out for ads on the site that may advertise products frequently classified as a PUP (Potentially Unwanted Products). Thoroughly research any product advertised on the site before you decide to download and install it.'

Following this will permanenty delete their Microsoft email.

Does he do this through his Xbox? As it’s only allowing me to change the email for my whole account through Microsoft

Hello Samantha how are you?

My name is Ezequiel I'm an Independent Consultant.

I suggest you get in touch with your ex-boyfriend and ask him to change his Xbox account email, he just creates another email for example a gmail and he changes his account email, quick and easy.