Yes...both cats we had neutered and fixed 4 years ago. The male cat has never stopped being the green eyed monster... jealous from the very beginning even tho' he gets tons of attention. He will bully the female if he can get away with it, but she's been pretty good at getting him back and standing up for herself all these years. He's packed on a bit of weight just recently due to winter snacking and so seems a little bigger, and it seems he's frightening her more.

Perhaps a strict diet for him and weight loss and she'll not be overwhelmed by his bulky shadow looming near the litter box and less fearful?

I wonder? Could it be as simple as that perhaps????