Cat picking fights

Hello all,

First time poster, and first time visitor. Trying to figure out what I can do to help my 5yo cat.

First background:

I got my cat while with an at the time live-in boyfriend 5 years ago. Since then the boyfriend and I have broken up and the cat and I moved into our own place. We get visitors, but not often and I've started dating recently again. 3 nearly 4 months now with my current boyfriend.

She's sweet, loveable, and nice. To me.

Over the last months, her behavior has quite rapidly deteriorated. He's never been alone with her, so I know he hasn't done anything to her. She growls, hisses, and swipes at him. She will come out of a "safe" room (i.e. food, water, snuggly places to sleep, even a 2nd litter box) to pick a fight with him and growl and hiss. I got in between her and him and got my shit rocked (5-6 bleeding claw marks).

The first time it happened we were literally just sitting next to each other on the couch and she came over to chill i thought and NOPE lets start some shit. (Shes typically standoffish with people but doesn't mind them as long as they dont go into any of "her" spaces.)

The problem is, its not just him. She is now going after anyone who comes into the house. My bestie, other friends, my mom. Anyone who comes in catches those paws.

First thing I did was go to get her checked out, $94- some updated shots and shes got no obvious medical issues.

A few weeks later and I took her back to the vet due to escalation of behavior. I demanded a urine test for UTI. They had to stick a needle into her bladder since she went nearly 34 hrs (7 am Monday to 6 pm tuesday) in care refusing to pee, eat, or drink water. Negative. No UTI. She's just pissed.

She won't calm down, I've bought diffusers, got her a calming collar (no lavender - dont come for me) and the only thing that seems to work is to entirely "cleanse" my house of any scent left behind. I gotta wash blankets, sheets, pillows, i personally even have to take a full-on shower - anything anyone has touched has to be scrubbed or she wont calm down. Hours can go by and she hisses and growls and tries to claw me if I dont. The only thing she seems to half tolerate is a shirt of his ive left out in a attempt to get her to get used to his scent (its not working well).

What do I do? I love her and want her to be comfortable but out of everything ive tried nothings working. I'm at my wits end and I don't know what to do.