The way I see it our spouses have proven their loyalty and devotion to us for decades. Sure, they messed up big time recently, but any new partner we hook up with can too... and they have ZERO "good" track record with us.
The key is if the WAS has truly repented and is ready to make it work. If they are, that's when the new M can be better than anything anyone new off the street can offer.
M: A really long time. Crisis: 5 years. She's still worth it.
Life is never made unbearable by circumstances, but only by lack of meaning and purpose. -Viktor Frankl
