Cramming two people together at the last minute for the sake of having a co-founder is usually a bad idea. Better to go solo than have a bad one, and the chances of a bad fit when you don't know the person beforehand are fairly high.
Add co-founders if there are business needs that are foundational to who you are as a company, and you need someone as dedicated as you are to manage those aspects. Then look *hard* for the right person to fill this role. Don't just do it because it's what everyone is supposed to do.
Be aware that choosing friends can also jeopardize the friendship if things head south.