How should I pay a Joint Venture partner?

I am in an informal joint venture partnership with a person who gives me well qualified leads for SEO services. So far it has worked out marvelously (2 converting leads) but I am not sure how to pay him. What I mean is I will be receiving a payment from the client for lets say $100, but my merchant takes a cut of about 3%, then I have to pay expenses. Do I pay him before any other expenses? Is there a good source for different types of joint venture methods? Based on what I find out I will be drafting a contract so he and I can begin a formal JV relationship. I appreciate any info you might have as I am new at all of this. Thank you!