He was destroying euphemism. If a marriage is viable and you choose to leave a partner who is willing to stay with you, you are committing adultery. There is no good language for it, no pleasant way to say it. I'm leaving a bad thing behind. Again, I want to be clear that this is not the unforgivable sin.
Restoration is possible.
Name it for what it is. Euphemisms do no one any good. Let's look now at verses 13-16. Most commentators put a major break between verses 12 and 13. The language of the text does not make it clear if the two passages are linked by time or place, but there is a thematic link.