The husband should have never said yes or that he would consider it to a threesome with his coworker. If he really wanted one, the idea should have been his and with no one specific in mind.

He probably should not have brought it up so close after her giving birth. Because it is her third child he should have known how emotional she is after giving birth and that you have to be a good father first before having a fun sex life in this critical time.

That said: the wife never spoke to him about her feelings. She signalled it very clearly by avoiding him but he didn’t get the message. She should have talked about everything and they could have worked it out.

In no way should she have ever brought up the threesome if she didn’t want it. Or have gone through with it.

The husband should have stopped the threesome the moment his wife was uncomfortable. Doesn’t matter if she says it would have not changed her mind that os set on divorce. That is the only correct way to handle the situation.

So the conclusion is: this marriage failed because of communication problems. The wife communicates through actions and mimic and gestures while her husband can’t read these at all and communicates through words only.