Changed Apple id password… what about email logged in on other devices?

If that email is your iCloud email then yes, changing your Apple ID password will require the new password be used to get your Apple email account on the other device. Anything that has to do with your Apple account on any device is connected to that ID. If it is a third party email service provider then that is independent of your Apple account password.

If you added your iCloud email account on his Mail app on his device it is using your Apple ID password for that. If you change your password then he will probably get an error message when calling up your account on his device. I am periodically required by my mail provider to change my password. I do so on my computer and when I go to my iPhone to read mail it says it cannot access my mail account. I can't remember exactly how I update the password and I think it may change with the iOS version you use. Anyway, it isn't difficult. I think maybe I just deleted the account from the Mail app and added it again with the current information.

I assume you are talking about your Apple ID email address and not your iCloud.com email. Changing the Apple ID password does not affect your email password that is maintained by your internet provider. You will still be able to get your emails after changing the Apple ID password.