If a man truly regrets the choice he made for his wife he needs to really evaluate the situation. Many people believe they are in love and later find out that the love they once felt is now empty. They may still love their wife but not be in love with her.
Life is short and must be lived with happiness! If you are not happy with your current wife figure out why. Many challenges can be concurred just by being open and real. Communicate about what is making you feel this regret, if your unable to find that lost feeling of love then move on.
Staying in an unhealthy relationship is never good and will only bring more challenges and problems. Moving on does not have to be a complete negative. Remember some people are just better off as friends. In any case always love and respect your spouse.