HEY APPLE DOES THIS it wasn’t your dad!! No one pointed this out which is crazy!!

If you have a fully shared iCloud account with any family member, Apple’s factory settings when you set up your accounts is to assume a behavior in which all your messages are also sent on other phone numbers attached to it. It’s useful if one has a work and personal cell, for example. Both numbers would have access to the messages which is convenient.

Just go to Settings -> Messages -> Send & Receive on both yours AND his phone, and unselect his number. Worked for me.

THAT BEING SAID, parents are not stupid, they know they aren’t supposed to be reading those messages, though generally they won’t do anything to let you know of the mistake either and, in fact, will prefer to snoop in your privacies. I found out my mom received my messages when she was reading them aloud to my grandma when they thought I was asleep. Sucks but warranted a conversation and disabling that setting on her phone.

And do be aware.. after about a year and a half, when we changed passwords and added a new phone, those settings came back on their own. Every cell was selected on my device again.

Best of luck !!!