What do you do when you realize one of your employees is a poor culture fit when you're a small startup and every employee feels so integral?
You address it immediately and help that person find a more appropriate fit. You'll both benefit in the end. Don't feel guilty - the faster you sort out who adds value around you, the faster you'll get to where you want to go. The only way you find this out is by trying each other out. It takes a great leader to recognize there is culture fit - and you can be sure you will recognize this in interviewing future candidates and not make this mistake ever again.