The title comes straight from dialogue in the story—repeated both at the beginning and the end. After the husband says, "Here we are" the wife replies:
"Yes, here we are," she said. "Aren't we?" (113)
This leads to a couple other questions: where are they? And where is "here"? We guess you could say that where they are is in the Land of Uncertainty. They haven't arrived at a conclusion about their marriage and domestic life—it's all up in the air. So the wife is wondering if they're really "here"—if they've really arrived, like a pair of quirky short story Moseses, in the Promised Land of Marriage, where everything is nice and calm and stable and everyone lives happily ever after.
It seems like they haven't actually arrived there yet, and it's unlikely that having sex for the first time will be the magic solution that puts everything together and makes them less likely to quarrel.