My parents both had affairs (no, they should have never married, but that was back in the days of the "shotgun wedding" - as the result of me
).
Their "speech" was that "we stay together for the child/children".
As one that lived through such a situation, my comment would be "Please, divorce for the benefit of your childern"....
My father had a "second family" for over 10 years (and I helped support them, by working for $0, at his "enterprise").
My mother didn't have one until she decided to leave, a couple of years before they finally split.
I'm through with both of them (one passed, one awaiting)....
Parents are so underated, IMHO...