Marriage is a non-linear story. In other words, your second one is different precisely, because the first one happened. Its a point we most often miss. Happy relationships are built on intimate understanding of human emotions, needs and flaws. Until we live in an intimate one for many years, we don't get the education required to make it really work. When we have the education, its no longer possible to repair the first one owing to the chinks and blemishes it has accumulated over the prolonged period of slow decay. This is the paradox of marriage. You have to have one, to learn to operate the other. But life is short. Our second chances are sometimes foiled because the fuel has run out, the emotional reserves are depleted, or a litany of difference factors accompanying the age. So blame it less on the imperfections of the earlier, rather the perfection of the later, enabled by that super-education. You can appreciate the luxury of the new, precisely because you understood the tyranny of the old. It could have happened (very possibly) the same way, if you flip the order of the two humans you chose !!!