Instead of pointing out what is wrong with him, you could highlight his strengths - sales and ask him to build on that. You could tell him that it'd be beneficial for your startup if you both concentrate on each of your strengths. You - the technical aspect and your co-founder finds ways to bring in mullah.

You must have a sit down and make sure you are both on the same page with respect to the capabilities of the product. If you don't have relevant documentation for the product you've built, perhaps he can work on that. This way he would understand the product inside out and at the same time have some material when presenting to prospective clients. Going through the codebase with clients is a big nono. Alternatively, you could ask him to prepare a demo of the product that he can use when presenting to prospective clients.

Congrats on building a product and selling it without taking loans and giving away equity! Great going