It is against the law for a state to deny a same sex couple the right to marriage. It is guaranteed by the 14th Amendment to the Constitution and the Equal Protection Clause.
The Equal Protection Clause guarantees that no person or class of persons shall be denied the same protection of the laws that is enjoyed by other persons or other classes in like circumstances in their lives, liberty, property, and pursuit of happiness.
This shouldn't even have to be a petition. African Americans and women have gotten their rights. It is time that homosexuals do as well.