I have a sibling who is planning to get married to a same-sex partner. I have been invited to the ceremony. Out of concern for the truth and clear testimony to God's Word, should I even attend? What would be the best thing to do out of Christian love?
We learn from Romans 14:14, 23 how dangerous it is to act contrary to our conscience. So, if you are convinced that it would be wrong for you even to attend the ceremony, then it would be wrong for you. On the other hand, you might be convinced that you can, in good conscience, attend the ceremony without supporting same-sex marriage.
It goes without saying that your attendance or absence from the ceremony is not the most important matter here. More important is what you communicate to your sibling about your presence or absence.
If you choose to attend the ceremony, you can explain that you will do so because of your love for your sibling, not because you agree with your sibling’s actions. If you choose not to attend, you can explain that you wrestled with how to show Christian love and also how to stand up for the truths of Scripture, and you settled on not attending the ceremony.
One thing to keep in mind is that if you choose not to attend the ceremony, there could be long-term complications in your relationship with your sibling; the opportunities for future Christian conversations with your sibling could be jeopardized. You will have to weigh your attendance at a ceremony with, potentially, many more years of contact with your sibling.
Christians will arrive at different conclusions to questions like yours. Their conscientious considerations account for the differences. God bless you in your decision.