Why is this such a big deal?

So, the guy may have wanted an “open marriage.” When my husband and I got married ten years ago, I told him I wanted to have an open marriage.

He said, “You do?!”

And I said, “Sure.”

He asked, “Really?!!!  An open marriage?!!! You and me?!!! An open marriage!!!”

I told him yes. I was sure. And what I meant, obviously, was that I wanted a marriage where we could tell each other anything.

That’s what an open marriage is, right? There’s no other meaning, is there? Because if there is, then I’m in deep s—t.