Cat Throwdown in Berlin

Hi, I just moved to Berlin from Colorado, and I'm living with my boyfriend. I have brought my 7 1/2 year old female cat with me. My boyfriend has a 8 year old male cat. Both are indoor cats and both are fixed. When I arrived, I made the mistake of allowing Cleo, my cat, to approach my boyfriend's cat, Simba. They sniffed each other and hissed at each other, but nothing else happened. Over the next few days, Cleo acted more pissed than anything, hissing and growling at Simba. Simba did nothing, just observing Cleo.
Then one day, Cleo slapped Simba in the face. A chase ensued and we broke up the fight. Everything seemed to be okay, until one day, Simba attacked Cleo 3 times in one day. Simba has claws, where Cleo was declawed when she was a kitten.
We started locking Cleo up in the living room for her own protection, since Simba decided to become so aggresive. I don't know what changed all of a sudden. He went from being calm and observant, to a total attack cat.
We only brought them together at meal times, and that was the only time Simba ignored Cleo, more intent on the food. Then a few days later, he attacked her again while they were waiting to be fed. A huge fight started, chasing Cleo from kitchen to living room, finally nailing her in the corner by the entertainment center. We sprayed Simba with a water bottle constantly, but he was totally unfazed. He took hair off of her. All my cat does is run for her life, screaming and hissing, and trying her best to fight him off. I guess it doesn't help that I'm hysterical when this happen, having a brain fart, unable to comprehend what is happening.
We have tried rubbing them with perfume and catnip, so they have the same scent, with the towels, allowed them to see each other through the crack in the living room door and then Simba still tries to attack Cleo through the crack. We have gotten the Bach Flower remedy that we have put in there food, and the Feliway plug in. Nothing seems to be working.
I have been here now for almost a month, and we are frustrated that we can't have peace between our cats. Simba seems to have a death wish for Cleo, and Cleo is just scared and wants to be with her mommy. We need advice on what we can do. Any suggestions?

Simba


Cleo

You're going to have to keep Cleo in a separate and safe place for a while, if not forever. Put her water, a box, her favorite pillow in the room and only in a week or so consider letting her out under your supervision for a short time. What would be ideal is to allow her out more often into neutral territory and Simba being in his own room for a couple of hours so her scent becomes part of the place and it's not just 'his' place. Don't spray either of them with water or perfume(!) as they won't 'get' what you're doing anyhow and it'll just make them crazier. You may not be able to change things long term however, as the dominating instinct in males is so hard-wired and you might have to consider either re-homing one of the them or else permanently setting up separate living quarters for either of them.