Homosexual marriage will devalue your marriage. A license to marry is a legal document by which government will treat same-sex marriage as if it were equal to the real thing. A license speaks for the government and will tell society that government says the marriages are equal. Any time a lesser thing is made equal to a greater, the greater is devalued. For example:
If the Smithsonian Museum displays a hunk of polished blue glass next to the Hope Diamond with a sign that says, "These are of equal value," and treats them as if they were, the Hope Diamond is devalued in the public's eye. The government says it's just expensive blue glass. The history and mystery are lost too.
If an employer uses a robot as an employee and treats the robot the same way it treats human employees, human employees are devalued. By doing so, the employer says, "A robot can do your job, you're no better." What will you and the public think of your job and you?
If the government issues a license to babysitters that grants them the same rights, protections and responsibilities as a child's parents, parenthood is devalued. The government says parents are just babysitters.
If government grants professional licenses to just anybody, every profession and qualified professional is devalued. The government says an uneducated panhandler can do brain surgery.