The real work of two people blending--the behavior stuff--is where things really get interesting. Because after so many years of being by yourselves, no matter how much "Us" paint you throw on top of it, the old "You" still shows through. And that's usually not a good thing.
A lot of guys think the highest compliment they can pay a woman is to treat her like "one of the guys". The whole "Treat others as you would be treated yourself" rule becomes "Treat others as if you were by yourself." They figure, "Surely we're beyond the silly formalities, the need to be civil. Let's relax. Be ourselves." And the women are thinking, "Let's not." Because we know where this leads.
While lying in bed: "Hey!!"
"Did you just fart on my leg?"
"Sorry. I didn't know you were there."
See, when you are by yourself, you apply your own standards. It might not bother a man to stand in the middle of the room, drink 32 ounces of club soda, and belch out everything you've eaten since Fall. His Self may not care. Others, however, may.
And if you're with another person all the time, like my husband and myself, every repugnant component of your life must, by definition, happen in front of the other person. There's nowhere to hide. Ever.
So you learn to accept each other. Your best behavior is now and forever reserved for outside the house, and once you're inside, you're free to be the repellent American you really are. That's an implicit understanding. "I know all about you, you know all about me, and it'll be our little secret."
You become a little team. It's the "two of you" against "everybody else". And you look out for each other. Your partner becomes the one person in the world you can go over to and say, "Do I have anything in my nose?"
That's your mutual job: protect your Ugly Truths from everyone but each other. Which is kind of nice, actually. Here is someone who will not only be honest with you, but whose love for you is so great it can withstand looking up your nose. And then they go right back to loving you as if it never happened.
It's ironic that Everybody Else--to whom you owe nothing--is spared from having to see what's in your nose. As if they deserve better. But your partner, the very same person you love more than all others, gets to look right in there and investigate personally. That's their little privilege. One of the many bonuses for signing on for the long haul.