Totally agree with all the comments about taking care of your health and managing expectations with your business partner. Trying to be practical though, you feel a commitment to "get the job done." Maybe try to think of ways where you can fulfill your role as technical lead and out source some of the development to contractors off odesk. There will be a couple weeks of inefficiency while you figure out the process, true, and then you should have a couple developers you can lean on to help you out. Your role will change from coder to product manager / architect. It's an uncomfortable transition, but I think worthwhile. If you want tips on getting through this process let me know.
