Hello. I'm a longtime lurker who needs some help/advice/constructive criticisim on cat behavior issues. I have two cats: a 10 1/2 year old orange tabby male named Pumpkin who I've had since he was 10 weeks old and and a 3 year old tuxedo female named Cookie who I've had for over two weeks. Both cats are neutered/spayed. Pumpkin's littermate Pepper (female) had been with us until May 2017 when she passed away unexpectedly. Since Pumpkin had always had a feline companion and seemed a bit lonely without one (and I also enjoyed having two cats in the home) I decided to adopt another cat. I had waited until January due to some health issues for myself and wanted the timing to be better. When I went to the shelter there were a few cats I was interested in but specified that I needed a cat that got along with other cats as well as one who was an adult, because I wasn't sure if Pumpkin would tolerate an active kitten at his age. Cookie met those requirements.
When I brought her home, I kept her in my second bedroom for the first nine days. I spent time with both of them separately and would rub their scent on socks and let each cat smell the others scent. There was some initial hissing but then nothing more. On their first introduction, there was hissing and growling, primarily on Pumpkin's part, but then he just walked away and they remained separated. The next day of introductions, Pumpkin came up to her, they sniffed noses, he hissed and then left. Their third interaction was in my living room: there was hissing and growling but no swatting or physical signs of distress or aggression. The following morning they were in the living room together again; Pumpkin hissed and proceeded to walk away to the kitchen. Cookie then chased after him and pounced. I made a loud noise and they each walked away. Pumpkin then went to go upstairs where the litterboxes are and Cookie chased after him again and pounced on him. When I got upstairs they were in cat fight posture; I didn't want things to escalate so I gave each of them a spray with a water bottle and then put Cookie back in the second bedroom since I had to go to work. I didn't want them unsupervised at that point. Things improved the next couple of visits and since Wednesday I've left them unsupervised while I was at work.
However, since Friday evening things seem to be deteriorating. I have three levels of home {first floor, second floor, and basement). There are litterboxes on each floor. Cookie had blocked Pumpkin while he was in the litter box on the first floor. Then, yesterday and today, I was gone for the morning and afternoon visiting my sister. When I got home Saturday, Pumpkin was at the top of the basement stairs and Cookie was at the basement door. The basement door was opened but he wouldn't walk past her to get to me. He always greets me at the door when I come home (he knows the sound of the garage door means I'm home). I got her food for her and then actually carried him upstairs. He stayed in the living room all evening. They would watch each other but I don't believe he hissed any. Their posture both appeared normal and non-aggressive. Today when I got home, Cookie was on the first floor, and Pumpkin was again downstairs in the basement, not even on the stairs just in the basement. I brought his food down to him and he started to eat. He seemed like he was ready to go upstairs and I tried to coax him back upstairs with his food, but once he saw Cookie upstairs he went right back down. She then followed and I heard some more hissing and then he proceed to hide in this small space under the basement stairwell.
I haven't seen any physical fights or seen any signs of fighting, but it's like she's bullying him or he's just plain scared and doesn't want to be around her. Back when Pepper was alive, they would fight some; Pumpkin would want to play but then he would take to far and Pepper would start growling and hissing. They would chase each other; she would even swat him and couple times and knicked his ear, but then the fight would be over. She was never scared to walk through her own home and neither was he. I don't know want to do. If he hides in the basement all the time, I can make sure his food and water is downstairs with him (again, there 's already a box for him to use) and I can shut the basement door while I'm at work if necessary. But, I hate to do that him. I'm getting to really enjoy Cookie but Pumpkin is my heart; I just love the little guy so much. Plus, he has medication for hyperthroidism that he needs to take twice per day and ibd medicine once per day. If he's hiding the stairwell, I can't get to him to give him his meds. I don't want even think about this not working out and having to return Cookie but I'm not sure how to resolve things. If you made it though this long post and have some suggestions I'd appreciate it.