What have you been doing for the last 8 months while he worked on the product. Hopefully you have built up relationships and other important knowledge that are

What have you been doing for the last 8 months while he worked on the product. Hopefully you have built up relationships and other important knowledge that are still valuable. If so, you should be able to make a compelling case to new prospective cofounder. Might be harder if you're just an idea guy. Good luck. It's a long hard road either way.