It's time to look at what can be accomplished with the resources you have. You may want to borrow money or find investors to help you grow the company because your partner has clearly proven that there is more demand than you can meet now. If you can group the customers so that one project team can design the features that most of them want, you may be able to meet the commitments, especially if you can outsource your production without having to hire and train new workers. Once the immediate panic has passed and you have a plan for dealing with the over-commitment, you and your partner need to work on your relationship and your job descriptions. You're not acting as a team right now, more like independent contractors.
Someone has to be in charge of the overall company.
Maybe you're not right for it. Maybe he's not right for it. If both of you need to stay with your division of labor, you may need to hire a manager who can handle coordination, budgeting and the details to keep the company as a whole running smoothly. Your company is growing and this is just a bump on the road to success. Finish grinding it flat and move on.