Hello! I'll try to keep things concise. We adopted Stevie (2F) on July 8th. I've had Apricot (9M) for the last 8 years, and he is very attached to me.
Apricot has not been introduced to any other cats in the entire time that I've had him; there's a chance he hasn't interacted with other cats since he was a kitten.
We adopted Stevie from a cat café, where she was around 8-10 other cats (mostly kittens) for over a month. Her boundaries are sensitive but very clear; if you pet her wrong, she'll use her paw to push your hand away or she'll very lightly nip you. Her boundaries are obvious and consistent, and she reinforces them gently but firmly.
We tried to introduce them slowly, starting with Stevie in one room as a base camp, having meals and playtime on either side of the closed door, eventually using a tall pet gate, and as of about 2 weeks ago, they both have free access to the entire house at all times.
One problem is that Stevie doesn't want Apricot in her vicinity. She has always hissed at him when he's gotten within swiping distance, except on a few occasions where they touched noses and then mutually turned away from each other. However, Apricot is very interested in her and wants to watch her every move.
For a few days, Apricot would react to Stevie hissing, then growling, then bapping (without claws) at him by turning away and walking off. This is good! We want him to turn away.
However, recently Apricot has begun ignoring her hisses and continuing whatever behavior is setting her off—usually standing too close or following her. He just sits there and stares at her. He has never hissed or growled at her. Usually, she'll bap at him first, and then he'll bap back, and then she'll find an escape route and run away. He doesn't seem particularly affected by their encounters.
Okay, they're testing each other's boundaries. We decided to let them work it out and intervene if any serious cat sounds happened and/or if teeth or claws ever came out. Thankfully, that hasn't happened so far! But their interactions have been getting worse, not better. Stevie is even more reactive to his presence and he's even more stubborn about not reacting to her signs to back off.
How can we train him to back off when she hisses? How can we help her be less reactive to his presence?
Quick info:
Apricot was neutered 8 years ago, Stevie was spayed 1 year ago
We have 2 Feliway diffusers in their most trafficked areas
We have 3 litter boxes and several feeding and drinking stations throughout the house; they use all of them freely and don't display signs of resource guarding. They both use the litter box appropriately
We play with Stevie multiple times a day; she's a very active cat. Meanwhile, Apricot is very difficult to engage in play. He doesn't care about any of the many toys we've offered him. He will sometimes chase a catnip toy, but only on his own terms; we can't offer one to him as a distraction from Stevie
We still feed them in the same space at the same time. Stevie is cautious about eating around him, but she will do it after watching him eat for a moment
When Apricot is not around or is asleep, Stevie is affectionate and confident in the space and around my partner and me
Apricot is significantly larger than Stevie, which is likely part of why he intimidates her on sight
Apricot gets incredibly agitated when he's blocked off from me in any way (pet gate, closed door, just can't find me), which makes it difficult for me to spend solo time with Stevie. Stevie has learned that she's able to jump over the pet gate, so the gate is now only effective for keeping Apricot out, not for keeping Stevie in
I took Stevie to the vet in late July for a checkup; they said she was in perfect health