Is it wrong that I'm afraid to have my crush and my best friend meet?
What do you feel would happen if they meet?
I don't think the two of them would get along because they have such different personalities, and I don't want to get caught in the middle.
It's okay to have and maintain different friendship groups. If you don't want to introduce your friends to each other, you can spend time with them seperately.
But he (my crush) loves it when we spend time together constantly, and he says he wants to meet my best friend.
If you don't want your friends to mix, that's okay. You should just explain to him that you want to keep your friend groups separate for now.