I synced my phone and another phone together with our numbers and now I can't unsync them. Please help.

I synced my phone and another iPhones numbers together so now we get one another's text. It's quite annoying. you can turn it off but sometimes we still willl gef each other's text or it will look like we texted other people. I want to permanently gef rid of the other number off of my phone. Please help.