Also keep everything very clear between the two. Document everything. My new co-founder is an awesome dude. Since day 1 our chemistry was great, however I got him to sign all the documents just in case.
Here is how things worked with my current co-founder. He wanted to help me build the product I was working on cause it was his passion. He gave me a hand. We didnt think of each other as partners. We just enjoyed working together. He got excited when his proof of concept was well recieved by customers. Then he started to committ take less shifts at work to committ to the project. He acted as my co-founder without even me asking him. Then we agreed to start a business and became co-founders.
Great guy! I love working with him! But to this day, I get everything in document so he knows everything is crystal clear.