When we started a product, we agreed to split shares according time spent on the product. For example, I worked about 40 hrs per week (we all had another (main)

When we started a product, we agreed to split shares according time spent on the product. For example, I worked about 40 hrs per week (we all had another (main) job initially), but other 3 people worked ~10 hrs per week. So in the end I had higher stake. If you both work full-time, this strategy will not help. However, you can find a measure of value. Maybe your partner is good at something else, like promotion and marketing. Then you should discuss responsibilities and maybe he can do some smaller features, but will focus on something else. If that will not work, I think you just can't keep work together, that will be a waste of time and a road to failure.