Banning gay marriage will do nothing to stop gay couples from living their lives in the exact same way as straight married couples, except, of course, when it comes to rights. We will still choose to bond. We will still choose to commit. We will still choose to care for each other until death do us part.
The effect of our living that way will still be felt in the society at large. It will encourage our friends and neighbors to trust they can rely on us more because we've "settled down". It will comfort our families to know we're being taken care of by someone who truly loves us. It will enable our straight married friends to relate to us better as we make similar decisions about property, socializing, and even children.
It will simply be labeled something different.