Well, let's talk about the divorce of the polygamist, does it disolve the entire marriage, or just part of it? Who then do the kids belong to? After 5 wives and 30 kids, who pays the child support, and how much?
Ok let's talk about straight heteros here then (of which I am one).
I could reasonably ask most of the same questions you just did about hetero-marriage and the same answers apply: The courts.
If you have ever studied entities under the law you will run across all kinds of partnership agreements and the law deal with all of them. If we take God out of the picture marriage is just a legal partnership agreement, but with special privileges afforded to those forming the agreement if they are 1 man and 1 woman. I like you don't want and I am opposed to special rights for ANYONE (I am against affirmative action in all forms) - but I staunchly support equality and fairness. That being said I am not for the legalization of "gay marriage" but I am for the redefinition of marriage and removing the religion from it.
Ever the secularist,
Jack