The short answer is they don't "snap" out of it. They gradually emerge from the thick and poisonous fog which has enveloped them - and it can take many, many months from the time the affair ends.

Me: 46
W: 46
T: 23
M: 20
DS12
DD11
DS5

W left: 01/28/08
Discovered OM: 02/26/08
W back for 9 days: 04/08
W returned 05/21/08
EA/PA - 01/08-07/09
W's MLC 2008-2014 (realised this much later)