Why, thank you... Though, you'll get a lot of libertarians disagreeing with you on that, when you hit foreign and defense policy.
Actually, the Libertarian (big L) position is to get government our of marriage altogether.
So if homosexuals wanted to marry, and they found someone willing to perform the ceremony, they could. However, it would not be state sanctioned, or have any legal force behind it. And in Libertopia, everyone would be free to discriminate, or stated more positively, freely associate.
There would be no laws mandating That Christian churches and businesses must hire transsexuals - or that bathhouses hire evangelistic Christians.