I was hoping to keep their existence a secret from each other until I had my male neutered but the neighbouring cat snuck up on me before I could shut the door and they came face to face (literally since standing on their hind legs they could just see each other's face through the screen).

I don't care if they are friends through the screen windows but I wanted my cat to see the vet first and get neutered. Now I shut the door but he slipped his way between the blinds and is sitting on the a/c meowing. I have 2 windows and a deck door that they will be able to see each other through so I expect they will do so.

Its kinda hard to tell whether they'll hate each other. Right now they are curious about each other and the cat across the hall, his tail was puffed out a bit. Now he's gone home and I'm letting Dustin perch on the a/c where he's making soft meowing sounds. Neither hissed, neither made that deep noise that sounds like it comes from the back of their throat that they make when they are upset. Tails are not wagging (which I think is a sign of agitation). Neither sounds like they are trying to intimidate the other.

I guess I'm just not sure about cats being neighbours. I have read about introducing a cat/kitten into the same home but I'm not sure about cats getting along as neighbours. I decided my cat would be an indoor cat because I feel its safest for him but I also considered the cat outside's feelings and his established territory. He's allowed out on her porch and the roofs are aligned that he can crawl all over the house. In a regular apartment building neighbouring cats wouldn't see each other but here they can.

Should I tell the lady across the hall about my cat since her's might start acting weird. I had no intention of introducing them because I'm not sure, if they were dogs it would be a different matter. Right now I'm letting Dustin sit in the window and see the other cat, who's moved off to the side and turned his back on us but I'm frequently going to talk to Dustin and pet him and reassure him. Fortunately he has a soft meow and isn't naturally noisy so he's not upsetting the entire house.

And, strange as it may seem, I'm worried that the other cat might feel some rejection because I got my own. I adore him but Dustin is perfect for me. But I used to sit on the deck and pet him and watched him for a few days while the neighbour was away on vacation. I'm worried I hurt his feelings. Am I being silly? Could I hurt someone else's cat's feelings? Does anyone have any experiences they can share with neighbouring cats?