You are thinking wrong. The odds of you coming out with what you think you are owed in this deal... well, we need C3PO to tell you with enough character to get the tone right.
In any case, I wish that people would find partners that they could actually, you know, trust. I am as cynical as the next guy, but damn people.
You think that this is a rational process?
He knows that he had this great idea and worked until he found a huge market for it. Sure, you did lots of work, but kids learn programming at the local JC and there are lots of them who do that web stuff. Besides, he'll soon find out that django practically writes web applications by itself. Sure, he wants to be fair, but you just sat around playing on a computer.
You're doomed.
All that said.. original poster, get everything formalized ASAP!