Cat all of a sudden hates someone...

Hello everyone!

I just moved in to a new place a few weeks ago. Before I moved in, my roommate was having problems. The cat, Harley, is an un-spayed cat that he took in after she had lived with some not-so-nice owners. This cat loves my roommate. He has been dating his boyfriend for some time now (many months), but a few weeks ago Harley started hating his boyfriend for no reason at all. Before that, Harley was perfectly normal and affectionate toward him. He hasn't done anything to hurt or harm her, and he hasn't been around any more or any less than he had in the previous months. He will walk in to a room and she will his and go crazy and run away. There was a situation in the kitchen (before I moved in) where he was cooking and she was just in there and she freaked out and peed EVERYWHERE and rubbed it on the walls. She has started taking refuge in my room now when Harley's original owner isn't here and it's just his boyfriend at our place. She is getting out of control and it seems to be getting worse. I don't think this situation has anything to do with me moving in because a) it started before I got here and b) she now takes refuge in my room when she is scared.

Why would Harley all of a sudden start hating her owner's boyfriend for no reason? Would getting her spayed help?

When was her last check up? Sudden change in behavior can mean a health issue. Also ask the boyfriend if he changed cologne or shampoo or anything that would alter the usual way he smelled. Maybe he is wearing something that upsets Harley.
Finally, spaying her is a good idea. But find what is wrong before exposing her to the stress of the surgery.

Also did he recently get a new pet? Or does he work somewhere where he is exposed to other animals?

I used to work as a vet tech and my cats used to get all upset when I got home until I changed my clothes because they could smell the animals on me.

Also when I take one to the vet I have to wash them down with a damp cloth before I let them go back with the rest of the cats because they can smell the office and other animals on them and start hissing at the kitty that went to the vet.

back when chloe was a baby and had just started to come out from her hidey hole, she had one other person that she would show herself to. as a matter of fact, she would sit in this persons lap, rub on him etc. it was a guy i was dating to be exact. mom and i were absolutely amazed that chloe was so open to him since she seemed to like him more thatn me lol

suddenly he started saying that as soon as i would leave the room, she would hiss and scratch at him etc. i found this to be odd since whenever i came back, she would be in his lap. i thought maybe he was jealous and was trying to subconciously make me get rid of her.

at night, she did start to hiss and growl at him and i never could figure out why. about a month later, he became abusive toward me and i learned that he'd been breaking into my apt and going thru my things, including my computer when i was at work. (he lived above me so no one thought anything about seeing him there)
chloe was the only one who picked up on his negative vibes toward both of us.

maybe the cat knows something the ppl dont --yet