One way to think about this is to translate your early work into a pre-seed round. How much money would you need to have raised last August to pay a contractor

One way to think about this is to translate your early work into a pre-seed round. How much money would you need to have raised last August to pay a contractor to do all the things that you have done? What risks were there as of August (technical risks, market risks) that you have solved or de-risked? And then finally, how much of the company would you have had to give up in order to raise that much money to pursue this idea? Take that as a starting point and give yourself that share of the company as if you were a vested investor who had funded this round. Then take the rest of the company and divide it up based on your joint forward-looking labor. Doing things this way can make it more clear who is being paid for what. It establishes parity in terms of how much work your both doing now, but it also gives you credit for the early investment of time and risk that you took on initially.