This applies to not choosing to believe as well. There’s a reason the Founding Fathers were inspired to place a separation of church and state in the First Amendment, it was to prevent religious beliefs, or teachings, from being forced on the general public in the form of laws. Thus, if limiting same sex marriage is based on religious beliefs, it’s not Constitutional.
Sometimes the hard part about living in a country with a Constitution like ours is being willing to protect and defend the rights of others to have the inalienable, God given right to choose how they will live their lives. In short, if you don’t mind religions telling other citizens – through the civil government – how to live their lives, I’m sure you won’t mind when other citizens – through that same civil government – start telling you how to worship.