If I change my Apple ID will that stop imessages from being sent to another iPhone?

I recently found out my ex was still receiving all of my imessages on his phone. While we were dating we had our phones set up on the same Apple ID account. I know that to stop the messages from being sent to his phone I need to go in and uncheck my number from "send and receive" but obviously that is not really an option. So if I were to just change my Apple ID would that stop the messages from being sent to his phone?

With imessage its designed to do that, so you can share messages between others and other devices too. Yes, you should sign up for a new apple ID and have your own ID for your phone, otherwise you 2 are still linked with the same account.