That's your interpretation of Genesis, and huge numbers of Christians (including my friend Esther) think your interpretation is wrong. Entire denominiations of Christians, including theologians and Christian Bible scholars, say that what you are holding up as a restrictive definition of marriage is no such thing. It doesn't, after all, claim to be a restrictive definition of marriage. It looks like a description of marraige that leaves out all sorts of other kinds, some of which the ancient Israelites practiced and that we never see condemned in the Bible.

For example, many Old Testament patriarchs had multiple wives and even concubines. That's certainly not "one man/one woman," is it?

So your passage could't be all that definitive.

Even if it were, see the rest of Esther's story.