[Hopey]

If you're going to do it, now's the time to do it. Your cat is still a kitten, so it hasn't gotten territorial yet. If you introduce another kitten, they'll spend all of their time playing with each other and will be used to each other by the time they reach adulthood that they won't try to kill each other at every opportunity.

I have two cats. They're brother and sister and we got them when they were about 3 months old. They sleep side by side when it's cold in the house, they clean each other, and they play-fight. Every so often they'll have a "real" fight, but it never turns into anything too serious.

However, there's absolutely no way they'd accept another cat into the house. They go ballistic whenever they see other cats outside, and literally throw themselves against the windows to get at them.

A few months ago we took my sister's cat in while she was looking for an apartment, and it was a total nightmare until she finally took him back. I had to ensure that I kept her cat and my cats separated at all times. The few times that they managed to get each other, there was blood spilled. My cats wanted to kill the interloper. I tried all of the tricks that I read online to bring in a new cat to a household, but my cats would have none of it. They were never going to accept him.