UTI - Tough to get rid of?

I have a 7 year old, fat, short-haired American domestic tabby cat. My big loveable little guy has had a bad UTI, as the vet described via urinalysis, for at least 3 weeks now. He's been on medications for his UTI, but he also has had the problem of crystals in his urine for about a half a year as well.
My question is, how long do UTIs usually last considering?

My heart is breaking because I've had to keep him locked in a little room with no furniture, and he wants out so badly. Poor guy is just peeing all over our beds and couches, though. We cleaned everything very thoroughly, but he keeps going back to the same spots to pee. My parents are ready to get rid of him, and obviously I just don't want that. They keep saying "he's not getting any better," but I'm convinced that he will! He's been on medication for 2-3 weeks, and he has always been on medication for his crystals.

How long will he avoid the litter box?
Is there anything I can do to help move his healing process along?

Any help will be greatly appreciated— I've spent hundreds of dollars on him, I love him so dearly, and refuse to lose him. He pees in very small increments, so although he is peeing, his bladder is not full.

When was your boy last at the vet? When was his last urinalysis...was he clear of crystals? If his last urinalysis was not clear, he should have another one.
Outside of a medical issue, sometimes after a UTI or bladder inflammation due to crystals, a cat will avoid using their littlerbox because they associate the littlerbox with the pain of the infection so they pee anywhere but there. If your vet has no concerns of a continued urinary issue, it might be worth trying a brand new box (different from his current one), new type of litter and in a new location.

I hope this helps. I have a cat with urinary crystal history so I understand how tough this must be you and your tabby boy. I wish you the best of luck. I'm sure others will chime in with their thoughts as well. [emoji]10084[/emoji]️

He does need to get checked again if he hasn't been recently.

A completely new litter box is good.  Also what did you use to clean the spots where he has peed.  An enzyme or carbon dioxide cleaner is needed to completely remove all remnants of the scent so he doesn't keep going back to the same spots.