Sudden servitude for Kotetsu, sounds like a plan. Welcome to the human world.
Kaede's hair color seems similar in shade to his second owner's. For a moment there I thought she was a daughter of that person, but if she was and Kotetsu didn't recognize her, then it means it has been ~15 years since his death as a cat.
So his owner moved houses, and he took that badly as abandonment. Not knowing people can often move houses due to any number of circumstances. His original owner was clearly not in a position to keep taking care of him, so he was put in the care of a friend. Then she moved places (the reason she no longer lives there could be much worse, but let's assume the most wholesome outcome), and he eventually met his end without seeing her again.
There's an explanation in-universe why only Komugi is a human with cat girl features, but I still feel cheated that Kotetsu isn't also a cat boy.