How can I find out if my iMessages are going to all devices
I have 2 iPhones on my account, one is mine, the other is my spouse. How do I find out if my iMessages are also being sent to his phone?
iPhone 6s Plus, iOS 10.2.1
If your AppleID is listed in: "Settings" > "Messages" > "Send & Receive" on his iPhone then yes, he is getting all of the same iMessages.
I guess the true answer to your question is that is that you would also be receiving all of his iMessages if you both have the same AppleID registered in the Messages App. So, are you receiving iMessages intended for him? If so, then he is also receiving yours.
If you are in a situation where you can not change the settings on his phone, then simply change your AppleID password.