We had outdoor cats when I was growing up. My one cat, Corvette, was a frequent wanderer. She liked to go visit other farms, and get other food, attention from other people. That was just the way she was. She was spayed, but that didn't stop her from being a nosy girl who wanted to go and investigate and hunt as well.

Don't give up hope just yet. He'll be back, and when he does come back... keep him inside!