Mimi wants to start an "only cat" club. She definitely prefers being the only cat. Adding a second one so late in her life was not a happy thing for her, and it still isn't!
But since your cat is so young, maybe it would work. The only problem is, you won't know until you bring another one home, and if you're like me, there is no way you'd take it back! LOL!
If Ritz isn't acting out, just doing things a little differently, she's probably fine, just being a cat! With Mimi, things have always been done on her terms, not ours. She can be very affectionate, but then other times not so nice. Tonight, I was holding her, and she was purring and snuggling on my shoulder, then all of the sudden, she bit my face! Butter was nowhere around, so I have no idea what was up with her.

Good luck. I know you want your snuggly, loving kitty back.

Logan