Has anyone regretted getting a second cat?

Sometimes I feel like my cat (2 years, female, spayed) would be happier if I got her a buddy. But I am quite thoughtful and I fear that I’m omitting a negative aspect.

Has anyone’s cat rejected the new kitten for a long time? Does the new cat pick up positive behavior traits from the initial one?

Any experiences are welcome!

EDIT: thank you all for your great advice! as of my take aways from your comments: 1. cats do not necessarily need another feline buddy, and they often don’t get along (which does not imply they hate each other) 2. fostering a cat to test my cata reaction is a good idea.