I think you're perhaps expecting your cofounder to approach problems exactly the same way you do. You shouldn't be looking for someone just like you to be your cofounder. Differences are often strengths.

What you need to be doing is looking for someone that delivers on the things you need them to deliver. Not someone that works in the same way and to the same exact schedule you do. My cofounder produces a helluva lot more code than I ever could, and he's always been part-time in the company (but he has equal stake, for a number of reasons beyond being an absolute monster at producing code).

That's not to say you don't need someone who will be all-in. You do. You definitely need dedication. But, it doesn't necessarily look the same as your dedication.