Correct, menopause for most women starts at 51, and ends after one year with no periods. It is accompanied by mood swings, hot flashes, a drop in libido, painful sex, etc.As your wife is 50, I'm guessing she is menopausal.
A time when women re-evaluate their lives.
If she wasn't happy with you or the marriage, then this is the time it will blow up.
Some women can have premature menopause, as early as age 40. Any start is normally genetic.
Peri-menopause normally starts at age 47, with irregular periods, spotty bleeding, etc.
The highest prevalence of cheating in women is at age ~37 after "7" years of marriage, the 7 year itch. The urge continues in their forties.
I like to put the blame on cycles.
In truth, it is a combination of factors. It is part of our natural age structuring that sets this behavior off.
It often is a last ditch effort to find a better relationship.
Of course, done so, while the woman herself, still feels competitively attractive.
Life is predictable.