[MalcolmDiggs]

When a friend wants to start a business with me, I just tell them my rule:

I don't work with friends, and I don't make friends at work. I keep those two areas of my life completely separate.

The benefits are: you can make whatever business-decisions are prudent without worrying about upsetting a friendship, and you can make whatever friendship decisions you want without worrying about how it effects your business.

I have a similar mantra for business & family, never mixing the two.