My hubby has done the same thing. Left a 19 year marriage for OW. He just walked away from 3 kids to live at her house with her son. He thinks he has feelings for her. I personally think long term relationships can get comfortable... and they got a taste of excitement with someone new and so they think that is love. I dont know if its a mid life crisis, but when they realize what a stupid choice they made, eventually that excitement will go away, they will have regrets. The choice for us at home is how long can we wait? Good luck... I dont post much..Im horrible at giving advise..still trying to take it!:)