Ask HN: When is a business cofounder absolutely necessary?

I'm technical and founding my own startup right now - it is vastly technical SaaS startup, but while it is very technical - there is a lot of work on the business end that doesn't meet my background.

I do have a little background in business (from college) but nothing that matters too much on the business from the real world (IMO).

Right now, I'm moonlighting my own startup and have focused for about the past 3 months now solely on the product. Before working on the product I did some market research, did a survey to my initial target audience, and have talked to a handful of individuals about it. All with pretty positive feedback once I thoroughly explained it (and no they weren't my best friends).

My question is, when is a cofounder (on business end) absolutely needed? --> I know optimally, the sooner the better, even 3 months earlier would have been better - but I haven't found a good fit so far. Any ideas?

If I could do it all myself, I would, but that is unrealistic for one person, while moonlighting :)

Thank you - to anyone with advice or thoughts on this.