> he told me that he believed the person staying should own everything that was created

That speaks volumes. He had absolutely no skin in the game, and didn't have any actual work to do to make the platform a reality. Why would HE ever leave?

It is pretty much a guarantee that if you got tired of doing the project, he would still own the rights to everything.

IANAL, but I watch a crap ton of Judge Judy... You are, right now, through this post, admitting that you had this discussion and that was the outcome and your continuation of work was "in agreement to his terms". The dumbest thing you could do in a situation like this is document that you guys had agreed to something like that.

You NEED a lawyer, and this post might have done some damage.