Many people think cats are not happy unless they are free to roam outdoors. This is so untrue, an indoor cat is just as happy.
It is proven that indoor cats live a longer life than outdoor ones. There are many things that can harm your kitty outside. Like cars, other animals & people. They are also more prone to picking up germs & diseases from outside & bringing them home.
Your cat should be kept in at all times & only allowed to venture outside with you when you have him on a harness & lead. Yes, you can train them to do this...(all 3 of mine do).
You should also have a collar & ID tag on your cats neck at all times in case he accidentally gets out. Cats don't like the feel of a collar at first, but in time they will get used to it. If your cat is the type to bite the collar off his neck you should look into getting him microchipped. Call your local shelter to find a low-cost microchip clinic. If you are lucky enough for some nice soul to find your wandering kitty, at least they will know where to return him.