There's often cultural pressure to take a co-founder. Don't listen to it. You are different, and what's worked for others is only a suggestion; never a rule.
Everyone should know that each partnership has one who works harder and brings more. You have to know, going in, that it might be you and how you would feel about it.
Finally, it's not your partner's fault the business plan isn't panning out; they never do. They exist to help you clear your thoughts, not to predict the future.