I thought we were friends
The ultimate insult you throw at someone you used to like. It means you're so stunned by their betrayal that you're ready to cry, yell, and maybe even throw a pizza at them.
I thought we were friends. Now I'm gonna throw my pizza at your face.
You said you'd never leave me. I thought we were friends. Now I'm gonna leave you.
I thought we were friends. You just called me a f***ing loser in front of everyone.