My fear is that if I start a company, my co-founder will drop out. How do you find someone to go through it all with you despite the challenges? I think it's difficult to gauge an entrepreneurial spirit in someone, especially knowing if they'll be able to tolerate the pressure.
Go on a long pleasure trip together before committing. Travel (eating and sleeping in the same place) brings to the surface the best and worst about people. In that sense, best honeymoons are those that take place before marriage.