How can I sync my boyfriends phone to mine if he’s signed into my Apple ID?
He’s more tech savvy than I am and he’s been messing with all of my stuff
You and your boy friend should immediately stop sharing an Apple ID!
Sharing an Apple ID only leads to confusion, as you may receive each other's text messages, etc. Further, the ID being shared is the one that will own all purchases, such as applications, songs, iBooks, etc. And Find My iPhone, and Find My Friends, etc. will become impossible to accurately use.
The person who gets the new Apple ID should immediately and thoroughly cleanse their iOS device(s) as follows:
If you can’t receive text messages from an iPhone - Apple Support