Um, could you take the kitty to a shelter? It would be more humane to have him euthanized than to be left out in the cold. Pleeaaase?? Even if you leave him in a carrier at the front door of an animal hospital before they open for business so he doesn't have to be outside for too long, they will take him in, and either care for him, or put him to sleep, whichever the vet decides is right for the cat. At least you won't have to think about him suffering if he freezes, or is attacked by another animal or is hit by a car. Please, I ask with the utmost respect for you and your girlfriend. It's one less thing to worry about for you.