Can't turn off iMessages going to my MacBook

I have never had my MacBook set up to receive iMessages since it is my work laptop. I did a Microsoft update two days ago and, all of a sudden, my MacBook started receiving iMessages. The iMessage feature on my MacBook has always been password protected and only accessible if I enter my Apple ID. How in the world did this get turned on? I'm not sure if the microsoft update and this issue are related or not but it's frustrating. I searched a YouTube video that showed me how to turn off messaging to my MacBook which I thought was successful but when the iMessage icon is clicked on MacBook, it asks for my Apple ID. When I click on skip setting up iMessage, it shows all my messages received the day things went awry. Today I am at a different location, different wifi, and my iPhone messages are going to my MacBook again! I turned off iMessage for today but what can I do so this doesn't keep occurring?

My previous messages (not the entire conversation history, but only messages sent the night before and that day) are accessible on my MacBook. When I delete them from my MacBook, they are deleted from my phone as well. How can I delete them from my MacBook without deleting them from my phone or is that possible?

Thanks for your help!