Despite the fact that it jeopardizes her happiness, I'm going to tell my girlfriend when I'm upset.
Is there a reason you want to share that with her?
I think it's time to move on and leave that relationship behind
Fair enough if that's how you feel. Being honest with them is the right thing to do.
I hope she doesn't feel hurt when I tell her that I want to move on.
It's good to be honest with your girlfriend and if ending the relationship is what you want then you need to be open and honest with her. It will most likely make her feel upset and sad, but that's natural and in time she will be okay. Just have a conversation with her in a manner that is respectful of her feelings.