Hello, I'm Dr. Deb and will do my best to help you today.
Unfortunately, if you've been working on trying to get Cocoa and Patsy to get along for a year now and been unsuccessful, you're not likely to ever succeed in getting them to like or tolerate each other. While most cats enjoy the company of other cats, there are some who would just prefer to be the sole cat or just don't like other cats for some reason.
If your fiance can't be convinced that this is not a healthy situation for Cocoa (or for Patsy either), then one last ditch effort would be medication for Patsy. Each vet has their own preferences, of course, but I usually try Prozac first since I've had some success with it.
If these were my patients, I'd probably treat them both since Cocoa is now hypersensitive and reactive to Pasty. Even if Patsy no longer is aggressive towards him, the mere sight of her will probably be enough for him to react. If she's more mellow and he's less anxious, then it's possible that harmony can prevail.
I always warn my owners though that long standing behavior of this sort may not be influenced by drug therapy alone although I have been faced with similar situations and it's worked out. Often if the aggressor (Patsy) leaves her target (Cocoa) alone, then a peaceful household may prevail.
I'd also suggest use of a natural pheromone, Feliway, which may to some degree help to reduce anxiety. It comes in a diffuser or spray and is often available at pet or grain stores or can be purchased online. I'm under no illusions that it will be effective in reducing stress by itself but it may be useful if you medicate them.
But, in my opinion, things can't, nor should they, remain as they are. It's simply not fair to anyone and not a healthy way to live for either the felines or their caretakers.
I hope this helps although I certainly understand what a difficult situation this is for everyone. Deb