Judges 14:5 Then went Samson down, and his father and his mother, to Timnath, and came to the vineyards of Timnath. 10 So his father went down unto the woman: and Samson made there a feast; for so used the young men to do.
In the instance with Samson, who insisted on being unequally yoked, the parents did attend his wedding after remonstrating against his course of action. And by so doing, they voiced their concerns, yet honored the institution of God-ordained marriage, because it took place within the framework of one man and his wife.
Judges 14:1 And Samson went down to Timnath, and saw a woman in Timnath of the daughters of the Philistines. 2 And he came up, and told his father and his mother, and said, I have seen a woman in Timnath of the daughters of the Philistines: now therefore get her for me to wife. 3 Then his father and his mother said unto him, is there never a woman among the daughters of thy brethren, or among all my people, that you go to take a wife of the uncircumcised Philistines? And Samson said unto his father, get her for me; for she pleases me well.
However, attending a gay marriage is different, for by one’s presence, a silent statement of approval is made as it pertains to same-sex unions and God will be displeased with such a course of action, on the part of the attendees, because by so doing, the very foundation of original marriage, and family life will be greatly undermined. The invitation to the gay marriage is given to secure your support, not your disfavor and therefore, if you were to accept and attend, it can, and will be taken for granted at face value, that you are in favor of the union that is to take place.
Deuteronomy 18:9 When thou art come into the land which the Lord thy God giveth thee, thou shalt not learn to do after the abominations of those nations.
May The Lord add His blessing to the study of His word. God bless!