I had two cats who lived together for 11 years, but they only barely tolerated each other, they didn't fight but they also didn't spend time together, play toge

I had two cats who lived together for 11 years, but they only barely tolerated each other, they didn't fight but they also didn't spend time together, play together, sleep together, or groom each other. So when one died I was shocked that the other paced around yowling for days. I don't know if he missed her specifically or was just confused about where she was and his confusion is what was causing distress.