Don:
If you are Roman Catholic and understand “holy matrimony” as a sacrament, then your attendance at such a religious travesty confirms your cooperation in the “error”, in the same manner that your attendance at the Eucharist confirms your “community” in your parish.
If you don’t agree that holy matrimony is of/at he same level as the Eucharist, then....you just might be Lutheran.
Regardless of ones Christian tradition, all have to come to grips with Ephesians Chapter 5.