I'm going to leave my girlfriend outside to wait for the train for an hour.
Why do you want to leave your girlfriend to wait for an hour?
It is cold out here at night.
Your girlfriend will be lonely by herself. It could even be dangerous to leave her by herself. You should stay with her to keep her company as she waits.
You are a slow reasoner. I just want to teach her a lesson for slacking off and not caring about me. If she is cold she can just wait inside the station.
That would be a mean thing to do. You're expected to support your significant other. If you care about her you should value her safety.