Heartbreaking confusion

We put the girl-cat to sleep today, and now the boy-cat - who lived with her for well over 15 years - is wandering around trying to find her. I keep trying to explain, or just to comfort him, and it's not working. He's not howling or anything like that, just bewildered and, I think, convinced he'll find her if he just keeps looking. Damned if it isn't making me cry.