Why does the sexual orientation of an individual matter to you? It is really NO ONE'S business what another person does in their "PERSONAL LIVES"! The fact is, we cannot control who we are attracted to or fall in love with, this has been proven in numerous psychiatric and psychological studies.
Whether you are gay, straight, bisexual, transexual, or whatever it may be it really shouldn't matter to anyone. BECAUSE that is NOT who you are as a person - it does NOT mean you are smarter, dumber, faster, slower, richer, poorer, kind, or evil, it is just a small piece of a bigger whole. Which in the end, is really what matters.
Why shouldn't gays be able to marry and more importantly why would it even be considered to nullify a marriage that happened legally prior to a law changing?
Would you want your marriage nullified by someone other than you or your spouse because of whom you chose to marry?
Think about it...