Look, either you're a priority in her life, or you're not. If going out every Friday to the point of not meeting your needs or being a flake on you because she's too tired is pissing you off, you need to say something about how you find it unacceptable.
Right now it sounds like you're not a priority, and you should probably let her know that this is what you are feeling. I'd say you've got a 50/50 chance of ending the relationship, but like I said, it isn't like she's actually making an effort to be in a relationship with you.
You can save a relationship by being the sole person to inject energy into it for a while, but after that it becomes draining and the other person's just an energy leech. Either she reciprocates, or you go find something better to do than visit her.
"Well, then," the Cat went on, "you see a dog growls when it's angry, and wags its tail when it's pleased. Now I growl when I'm pleased, and wag my tail when I'm angry. Therefore I'm mad."