I think it's with cats like with humans - some get along and some don't. I can imagine how difficult it must be to bring a new cat home, who you fell in love with but who your resident cat can't stand the sight of. It would be so much easier if you could take different cats home and let the one you have choose his new friend. Then, it would be hard to bring back the other ones. OK, enough blabbering!

I wish you luck finding Calvin new friend.