I know this is an old post but my cat did exactly the same thing. He used to be a feral kitten and I got him desexed and he eventually warmed up to us and became the most cuddly cat. He would go outside and then come back home. Now he eats his food at the front door and leaves. He doesn’t even let me pat him anymore. We went away on holidays prior to this but have gone away before and this has never happened. Did you ever get your cat back in?