I'm going to finally tell my friend I can't pretend to be happy for them and their boyfriend
So you really aren't happy for them?
No, I am not happy with their relationship.
Well, you don't have to be happy for them if that's your decision. Better to be honest than hide the way you feel.
I already made an attempt to be happy for them and their stupid boyfriend
Just give yourself some space from them. I think you need someone in your life and stop thinking about them.