They can live for years with urinary issues. An otherwise healthy cat can live with a UTI, or other minor (although painful and uncomfortable) infection for ages. As long as no secondary infection or issue crops up there's no guarantee it'll go away magically by itself, or that it will get worse and kill him...BTW the fact that your argument LITERALLY is "well he's still alive, so it must be ok" is incredibly flawed and ridiculous. Not to mention sad for your cat!
On top of that cats are well known for masking symptoms until something is horribly wrong. So the fact that he 'seems fine' is also not a valid argument.
Jitzu had a UTI for about a year before I caught on, I didn't know anything about cats at the time and we just thought she was mean and hated me...then when I got a bladder infection it clicked. My thought process literally went like this:
"My back hurts SO BAD! I can't even move
come cuddle me mean kitty. Ouch! Why are you always mad when I touch your back?" *lightbulb*
Sure enough, as the vet told me the symptoms it was like checking off a list. Grumpy/irritable all the time, drinks tons, pees tons (to be fair I had no comparison of her healthy behaviour, so some of this was only obvious in retrospect), reacts painfully to touch just above hips where the kidneys are located, pres EVERYWHERE, especially on soft things and plastic bags.
If you haven't been to the vet the rest of this work is pretty much moot. You need to be sure its not medical before moving on to the next steps. Also, (pet peeve here) f its recurring just because it WASN'T medical before doesn't rule it out NOW.
...get him tested. Bottom line.