First, don't do this, you will loose your friend and your business, a lot of times you will give your business to your friend before its over. Money changes people.
Second, make DAMN SURE everyone's responsibilities are defined and there is accountability for the work getting done.
You friend will screw your eyes out in many cases, because after all, you are his friend, obviously he does not expect to be treated like an employee or worker. If he decides to let something slide, it's no big deal to him, because you are friends.
If you partner up with someone, they can put you in debt. As a partner he may decide to take on some business that you do not want, and if he signs on the dotted line, guess what? You are obligated to honor his contract.
And what do you do when someone wants to do something you don't want to? They can just go ahead as an officer of the company and you get sucked along.
If they make a mistake or do something stupid, you pay for half the damage.
How much better it would be if you helped your friend start his own business,maybe doing something that benefits you and him. He can supply something you buy regularly, or subcontract jobs from you.
In this case, you have control o your business, and he has his.
Do wherever you want, but this is a disaster waiting to happen.
Having said that:
There are a few real friendships out there that really can come together and make it work.
I speak from experience on both accounts.
Lastly, don't do this.
