You probably shouldn't quote anything from Leviticus and try and wrap it around the idea of Christianity. Nothing from the Old Testament is taken seriously by Christians anymore.
As for gay marriage, I think marriage should be taken out of the government altogether. I don't think marriage should have any legal or tax connotation in the slightest. I think it should be 'government recognized union' or something. Then people can marry men, women, queers, dogs, dolphins, whatever the forget they want. Christian marriage can stay where it belongs: the church, and it can keep it's ancient traditions.
(this ticks me off)