Marriage is not a right, any more than driving a car is. You have to qualify. Gay people do not qualify, and by definition they should not qualify. Their issue now is that they are trying to change the standard for their own benefit.
I don't know how to answer you in the legalise you seem to crave. If it is discrimination, it is necessary to protect the institution of marriage.
Both marriage and driving a car are rights, in spite of the present governemnt tyranny to the contrary. You know nothing of liberty and freedom--no wonder we've fallen so far into statist oppression...