You need to get your cat neutered ASAP. Especially since he's an indoor cat, and he's already 5 plus years old. I don't know how you've managed to stand the spraying that all male cats do to mark their territories if they aren't neutered, and for 5 years, no less. The smell alone would have driven me up the wall- I hate the stench of cat piss. But aside from this, it's irresponsible NOT to neuter a male cat if you aren't planning on letting him breed. Neutered cats LIVE LONGER and are FAR HEALTHIER than their unneutered counterparts. You aren't doing your cat any favors at all by keeping him entire. Just the opposite, in fact. Unneutered males are at risk of prostate, penile, and testicular cancers as they age, just like human men are. They're also vulnerable to serious UTI's that often are drug resistant and very hard to treat. And there's another issue as well. Neutering your cat will eliminate his urge to roam, and will stop him from trying to get out of the house in order to go find a female to breed with.
Don't go believing the old wives' tales about how neutering a male animal makes it fat. If your cat gets fat after the surgery, it's because you're FEEDING HIM TOO MUCH FOOD, and he's not getting enough exercise. The surgery itself is NOT to blame for this. You also aren't depriving your cat of anything by not letting him have sex. He'll be much happier with his nuts removed, in fact. And I think you'll find that he'll be far more playful and affectionate than he is right now, because he won't be distracted by all those hormones pumping through his system.