Quite aside from that, though, I'm still not seeing any reason to assume that relationships in general exhibit this problem - only that it's not quite as uncommon as the highly atypical nature of my own experience led me to surmise.
(Or what I hope to be the highly atypical nature, anyway. If marriages like mine are anything except vanishingly uncommon, that's a serious problem. There are so many improbable circumstances around the way mine started that I've seen no reason to assume many similar relationships exist - but on reflection it occurs to me that I've failed to account for the possibility of stochastic convergence.)