Hi Randy, I hear you. My brother had 17 years of Catholic education, was an altar boy, lecturer, etc., married Protestant, and is raising his children Protestant. It breaks our hearts. However, there was time when he was a lukewarm Catholic and his wife brought him back to a healthier relationship with God through her faith life. So, I try to focus on the good that came out of it. I can understand why you would have a hard time attending the wedding. However, the Lord knows your heart and your reservations. The words of St. Thomas Aquinas may apply here - "to convert people you have to take them by the hand and guide them". I think this means that we need to meet them where they are at. Will pray that your son marries in a Catholic Church. However, if he does not and lives as a protestant, know that the foundation that you and your wife laid can never be lost. I can see it in my brother and have faith that one day, he will, too! Blessings to all.
