I've been experiencing the same issue and going at it for 4 yrs so I know your pain. Originally from Canada but am now based in Europe so happy to talk things through.

Finding a co-founder is hard. Finding a good co-founder is even harder. It's less about the product and more about the motivations for wanting to build something on their own. I reckon you'll need to dig deeper into the whys of someone wanting to start a business.