I agree. My dh had this problem before I married him and before I knew him. His mother got remarried and he told her that she is still married to his dad. She left the Catholic Church long before she got remarried and hated the Church. My dh and my MIL’s sister, who is also Catholic, struggled whether they should go or not because of their belief and Faith. They both consulted two different priests and both of these priests said that by going they were not saying that they agree with the marriage, but that they were there to show their love and respect for that person. Both my dh and his aunt showed up at my MIL’s second marriage. My dh has always told his mother that she is in adultery but she disagrees. She was happy to see both her sister and sons, all three of them, at her wedding. My husband still celebrates his parents wedding anniversary but he keeps it to himself and prays for his parents. His dad just remarried after about 17 years of being alone. DH did not go to his wedding, but it was because we could not afford the trip up North.
I do know how you feel for I struggled also when my cousin, who claims to be a devout Catholic and even works in Catholic Charities, married a man who is divorce outside of the Church. She was a virgin when she married, but unfortunately, she is living in adultery. I did go to the wedding, but went to show her my love and respect. She knew I disagreed with the marriage and most important that the Catholic Church did too for that is why no priest would marry them in the Church. Her fiancee did not get an annulment and in fact is not Catholic, so he sees no need for it. Now that he has her, he won’t get one. I know she told me that one day she will get married again in the Church when her “husband’s” annulment goes through. Her so call husband has not even filed for it either. Living in this sin has caused her to break other laws and one was on birth control. She was on it for a long time but now they want a baby and can’t seem to get pregnant. The sad thing is that she is still receiving Communion. I was told not to judge her and love the person not the sin and that is why I went to her wedding.