You did triple mistake i.e. an extramarital affair, with young girl and that too a girl with history of multiple relationships! Each extramarital relationship has an expiry date and your date has come. Woman much younger than man tend to develop other relationship quite frequently. Looking to these facts, I’m not surprised about what has happened. Only thing left with you is an acceptance. You cannot bring back someone to your life forcefully or by throwing emotional tantrums. Learn to live without her.