I'm a vet and an animal lover but I totally understand your frustrations. Problem behaviours in pets are the leading cause of death (due to euthanasia) in dogs and cats. Most likely it is the other cat that is causing the problem, it doesn't sound like a uti or kitty litter problem. Behavioural problems are tricky - they generally take a lot of effort in changing problem behaviour patterns and medications and pheromone diffusers can get expensive. It doesn't sound like a viable option in this case due to both finances and the cats personality.

I have NEVER in my career judged someone for making the decision to euthanase because I'm not in their shoes so I can't judge them for the decisions that they make. Though I have adopted several pets that were to be euthanised.

I'm very disappointed in the negative posts that are in this thread, we are here to encourage each other not condem each other.