I have sort of an interesting situation, and we've tried a lot, but I'll try to be brief.
I have a cat named October, and my girlfriend has a cat named Glory. Before she got Glory, October would visit her apartment sometimes, so he was familiar with the place. She got Glory, and a few months later I moved in with her, with October. October is male, neutered and was a year and a half when this happend, and Glory was 8. She had spend most of her life living in a dog kennel, where I worked, this happened because she was found on the street with a broken leg, the owner of the kennel took her in, for 8 years, until we adopted her. October was born of my friends cat, I took him in at 6 weeks of age. So, at first October just seemd playfully curious of Glory, and all she did was hiss and run away, she was very dramatic, but he never attacked her, just started at her, would walk up to her slowly, but he kept his distance. He slowly over the next few months started showing some aggressive behavior, chirping at her, flattening his ears, flicking his tail, etc. Then the first fight happened, and he was relentless, he was on top of her biting her neck, but not hissing or making any noise, while Glory was screaming her lungs out. We separated them, tried reintroducing them with carriers, through the glass window on the patio, we tried Feliway, feeding them at the same time, got a harness for october and have him on his leash in the same room, and on and on, but mostly we just have to keep them separated at all times. Lately things have been changing some, because while Glory used to run away if she saw him at all (especially when we have him on the balcony and they can see each other through the glass door), but now she is very eager to get to him, they paw at each other on the glass, they roll on their backs as they are pawing at each other, he doesn't make any noise except chirping sometimes, she hisses a lot, but if we open the door even a crack she runs away. Any idea on what she is doing? It seems like she just wants to start some drama, but that's probably just humanizing her, I don't know, this is my first experience with cats. Any advice would be appreciated, thanks!