Harry over at Crooked Timber outlines his thinking on divorce and gay marriage. Not original, but certainly worth revisiting.
The dominant public reason is that gay marriage will harm the institution of marriage. Suppose this is your reason for opposing gay marriage. You could still avoid the charge of hypocrisy by believing that divorce does not harm the institution of marriage, and hence that one’s own divorce has not harmed the institution one is defending. And, indeed, despite very high divorce rates, people continue to get married, so this isn’t a crazy view. But it does seem a strange view for conservatives, who are the main opponents of gay marriage, to hold. I presume that a conservative about marriage holds an ideal that marriage should be for the lifetime of the shorter-lived spouse, and that practices and behaviors that undermine that ideal damage the institution. Surely divorce does that; and, in particular, surely one’s own divorce does that.