I'm a single founder as well. I've learned the hard way that even those who initially seem to have the same drive and capabilities as I do usually don't in the long-run.
I started my first two companies alone, then started a third as a partnership with three others where I was a silent partner, then closed down my first company, then brought in a co-founder for my second company and renamed it, then took over the third company (the partnership) through buy-outs, then desolved my partner for the second (renamed) company.
It's kind of confusing, but the punchline is that every single co-founder who I at one time had a lot of confidence in has not held up their end (all of them admitting they hadn't at one point or another).
That being said, I would love to start a company with someone who shares my drive and capability.