So you are probably not losing a lot with going away, even if it's quite likely that they won't be happy with you breaking up with them.
That said, don't think too bad about them, because they are probably just inexperienced and don't know it better. And also don't think too high of yourself. If you are the only coder in an IT based start-up it doesn't matter who you are on paper. You have one of the most powerful positions. If you can't get it going it's also your fault and probably even more then it's their's, because you actually have the basic skill set to create software.
Another tip I want to give you on your way: Ask for a position as valuable as your leverage in the company. If you are the only coder in a software- or web-company you should definetely become a co-founder with a decent share of stock and decision making capabilities, maybe also CTO (CO often is more of a management job the moment you get more employees, so it's not required that an engineer does that. Someone with a management or business background might be better suited, even if the is a T).