If a loved one invites me to their same-sex wedding, can I show love by attending the wedding, or would attending communicate that I agree with same-sex marriage?
The 2016 Synod of the Christian Reformed Church addressed your question directly, stating in its pastoral guidance to the churches that it was acceptable for CRCNA members and officebearers to attend a same-sex wedding. Attendance doesn’t indicate agreement with same-sex marriage. Of course, some people may assume that attendance indicates agreement. But we can easily think of parallel scenarios where attending a ceremony doesn’t necessarily indicate full agreement with what is happening. Many a parent has attended a wedding where one of their children was marrying someone of the opposite sex of whom the parent strongly disapproved, perhaps even to the point of being convinced that the marriage was doomed. Attending is a way to show support and love for one’s child, not necessarily agreement with the marriage.
However, Synod 2016 also stated that playing a more formal role in the wedding likely would be taken to indicate support for a marriage that the denomination regards as unbiblical. Its advice was that church members should be aware of this risk when they play a role in a same-sex wedding, and officebearers should avoid playing a role because they would be seen as operating out of their ordained office.
Two distinct (though related) senses of “support” are involved in your question. There’s support in the ethical sense—whether I agree or disagree on a moral issue. And there’s support in the interpersonal sense—showing love to a person I care about. The view of Synod 2016 is that support in the interpersonal sense at a same-sex marriage is acceptable, but support in the ethical sense is not.
If you disagree with same-sex marriage but you support (in the interpersonal sense) one or both of the partners in a specific same-sex marriage, you would have to discern how much you want to go out of your way to indicate that you don’t actually support it (in the ethical sense). With all of this, you may find yourself in the complex position of praying for and supporting the partners in a marriage you don’t support.