Your girlfriend is just as human as you are. She is not a God, and you should not treat her as one.
The world is a bunch of imperfect people. We are destined to let each other down one way or another. We CANNOT put our hope in each other. If we do, we end up depressed and wonder why this or that person did this to us. It's becaus people suck! So we can't be suprised when they hurt us.
Your life does mean something without her. I obviously don't know you, but I do know that you are loved by God and that in itself is reason enough to live. I would get down on your knees and ask God for direction. He will answer. It depends if you you want to follow the road he reveals to you or not.