I think the bolded text nails it.
I am a strong believer in God and a Christian. I do not support gay marriage, because of what it says in The Bible - That God created marriage (my belief) for man and woman and nothing else. In addition to not support gay marriage, I don't support things in the same category (divorce, adultery, etc.)
Now, it gets very very very hard when looking at gay marriage. I see being gay as a sin that people are born with and they choose to fall-in to that sin. Similar to pornography addiction, alcohol addiction, etc. Most importantly, The Bible views all sins the same. So, although I do not agree with it or support it (just like I don't agree with pornography, alcohol addiction, etc.) ....I am not better than those that are gay. I sin just like everyone else does. Who am I to say you can't do this/that if I am doing certain things that are viewed in the same light (since all sins are the same) as this/that?
It's tough. So, if it was up to me, marriage would be man and woman. But, it's not up to me to judge.