There are some excellent posts on how to select a co-founder and what qualities you should look for. I firmly believe in 'try it out', and have been for about 5 months. In that time I've also come to believe that the intense start-up partnership is indeed 'like a marriage', although it may be unfair for me to slander marriage without giving it a try first.
I don't need to tell readers here that the requisite levels of day-to-day communication, agreement, and coordination are nothing like the corporate workplace. Some conflict is unavoidable, and disagreements have the potential to get personal in such a high-intensity environment.
While there's certainly some subjectivity in the question there is room for concrete answers. What are the tell-tale signs a partnership isn't meant to be?
What problems are big enough to warrant dissolving the partnership rather than working on the problem?