Many years ago, I heard the story of a man whose business partner did dirty. They were business partners for almost 5 years and the suddenly the business partner left with company's money. Even after several years, this man didn't recovered. He ended up sounding it as a warning to his kids never to go into business with anyone. The trust was destroyed and never recovered. This is just one of those sad stories.
That's the risk of having a partner when you have business. Because there's always a possibility for the other to have a change of mind and become greedy because of money. The reason why if you'd like to build a business with a friend, make sure you know him inside and out as one that you can trust and rely on.
On the other hand, there are many success stories of friends who went into business together and succeeded to together. If you have ever gone into business with a friend, what were your biggest concerns and how did work through it.
Aside from the skills and knowledge on how good he is in the business that you'll build, it's important that you are comfortable with the person. You can share ideas, criticism and open to each other. In short he should be someone that you can trust, much better if you known him for a long time so you already know what kind of person he is.