How to divide mortgage payments as equitable contributions?

[Nicholas Field]

I'm in a development project with someone. We bought the property together. It's his project, his name is on the mortgage and what not, but I gave the money for the down payment and it's every intention for us to do a development together. 

The property currently has a home on it. That home is being rented out. The rent goes to him and he pays the mortgage. He is saying the mortgage contributions he's been making are his equity on the project. 

I would assume the income from the property is project revenue, and not his personal revenue. 

Of course this wasn't discussed prior. This seems to obvious to me, but I would like some opinions. 

Thanks,