I'm breaking up with my depressed girlfriend on her birthday.
Why would you break up with her on her birthday?
She always tried to pull me down, I want to tell her something really hurtful to make her feel bad
Just because you are hurt does not give you the right to hurt someone else. If you want to break up with her you should do so respectfully and not hurt them.
I'll show her.
I really think you should just consider how she feels before going ahead and doing this. Because it's awful to break up with anyone on their birthday.