The fact that the children had already become adults, marry and leave the family home. Spouses, for many years used to living with children are alone with each other and do not know how to behave and what to do. Whereas previously they were kept in wedlock, now this bond bonding factor is gone, so he felt that marriage outlived its usefulness, the couple prefer to leave. However, this view of marriage is totally wrong: on the contrary, the husband and wife finally had the opportunity to be alone, without children. Remember, because as a young man you've probably dreamed of such freedom!
Think about that now you no longer have to bear and raise children. Remember what you wanted to do, but did not succeed. Maybe you've been dreaming about traveling, but could not because there was no one to leave the kids? Maybe you would like to move to another city or even in another country? Make desired, and you will once again feel the newlyweds are in love and happy. Now that the kids brought their families, as you become more experienced and probably richer than the young, the time has come for the fulfillment of desires.
Be patient and affectionate with your partner, know how to listen and hear, understand each other and to make concessions. Try also to diversify their intimate life: for such experiments is never too late. Think of all the brightest, most good things in your marriage and love my husband again for the happiness that he gave you.