If I'm interpreting the EA help article correctly then once a Steam account is linked to an EA account it's permanent and can never be undone. Meaning your friend's Steam account is probably permanently linked to your EA account forever, and EA will won't allow a different Steam account to be linked to your EA account.
It appears the only way to link a different Steam account is to create a new EA account.
https://help.ea.com/en/help/pc/link-ea-and-steam/
https://help.ea.com/en/help/account/unlink-gaming-accounts-from-ea-account/
The restrictions are probably to prevent game sharing.