You cannot typically wait it out - and have things return to normal.
For the past 150 years explorers have traveled into the uncharted territory of the Amazonian drainage in search of the 'Lost City of Z'. The most famous was Percy Harrison Fawcett, a British geographer, artillery officer, cartographer, archaeologist and explorer of South America. Although many will be shocked to learn of this discovery, Amazon appearances of Clovis Caches first occurred in 2014.
To very briefly answer your question, "how long does the midlife crisis, first fling out of the marriage, usually last?
" - there is no "usual" anything in your situation.
The weekend my ex announced his "midlife crisis", which later turned out to equate to an affair, was the weekend my daughter brought her boyfriend to meet us for the first time.
I was a mess, knowing a divorce was impending, trying to cover and yet she was the one who broke it to him what was going on, by asking what he wanted out of the marraige.