Live your best life and let others live theirs...
Marriage is sacred?
Fine.
That's God's business, if God cares to do anything about it.
I think not telling your SO can be disgusting, sure. The wiser, braver, and kinder thing is to stop wasting your (common) time and energy on unrevealed behavior and desires and get on with explaining how you feel and what you think you want to do.
Yes, it can be disgusting, but it's more sad, I think. Sad because some poor guy got himself into a deal without, perhaps, fully understanding himself, or, trusting the person he's with for, er, life. Play your cards and live your life. Perhaps that's God's plan for you...
My policy, after my first wife said, "Oh? That's all that was bothering you?" is to just get my thoughts and feelings out there early and often. She unloaded a ton of dresses on me when we divorced (about something else entirely) and I wish I had had room to keep all that stuff.
My second wife, now deceased, was slightly worried about being "outed" at work because of what I was doing, which I thought was both sad and hilarious. I think they would have said, "Man, you must really love this guy to keep him around with all that going on." She would have said, "Well, he's not just tall in one direction..."
People pair up and stay together because they know the other person, and know themselves, and they want to be together. Being open about yourself may close some doors, but it can open others... Be optimistic, not desperate.
Preachers, churches, states, and laws can't really stop "pairing" behavior and the rules within churches and within states are to regulate this fact of life as best can be done from outside a relationship. For example: "If you have problems, we'll try to help you work it out... somehow. Even if we have to beat you up to do it."
The odd thing about the gay marriage thing, when you think about it, is not that people want to marry, but that they want to marry even IF they don't legally have to, or, have a right to...
I get the desire to get married to someone, I just wonder if the former "gay lifestyle" is going to vanish when one half can start saying things to the other half like, "Look, either we get married and do this right or you can forget about ever having sex with me again."
Welcome back to the "wonderful" 1950s - and perfect families.