Honestly, it sounds like the ship have done gone sailed. If it's as dire as you indicate (which I have no reason to not believe), sounds like you need a lawyer.

It's also my belief that 50-50 partnerships turn out like this more than they don't. I've made a point to never get into a partnership. Sure, I'll work for someone else, or I'll have someone work for me. But 50-50 means there's no good resolution on opposing business decisions.

But my critique doesn't really help you after it's done. Check the contract. See if there's a buy-out option, or offer to sell your interest. Regardless, you're bringing in a big gun.