Well, that's where you're wrong.
Neither instance is "equal", and you can argue the equivalency all you want.
Men can marry someone of the opposite sex. Women can marry someone of the opposite sex. Gay men can marry someone of the opposite sex. Gay women can marry someone of the opposite sex.
Seems pretty equal to me. Fairness is another issue, simply because a man-woman marriage probably has more emotional significance to a heterosexual couple than a homosexual couple.
I'm going to give a little scenario... bear with me.
A nice family sits down for breakfast. Tommy and Timmy sit down at the table ready for their daily Cheerios. Mommy serves them all Cheerios! Once Tommy sees the Cheerios he screams out, "I want Frosted Flakes! I don't like Cheerios! It's not fair!".
Well, unfortunately for Tommy, it is fair. Both kids get Cheerios. It's too bad for Tommy that he doesn't like them but Timmy does. If he wants something else, he needs to get Daddy to balance the budget to buy his Frosted Flakes.
Nobody is getting any more than anybody else in this situation or in real life. Everybody can get married to someone of the opposite sex. It just means more to certain people.
I find it hard to argue that this ruling is legitimate, but a similar ruling based on gender or sex instead of race would not be legitimate.
Years ago...
White women could marry a white man. Black women could marry a black man.
Is that equal? No. I think we all know that. But let me apply the same logic to sexual orientation that you claim proves your point.
Straight women can only marry straight men.
Straight men can only marry straight women.
Gay men can only marry gay men.
Gay women can only marry gay women.
See. The scenario is actually quite different.
I think most of us know that many people feel just like many did in the past centuries. It's tough not being able to marry the person you truly want to marry.