What would you do if going to a family birthday with people you love a lot meant you would be around a gay couple? Half of our family are not Christians and will say we are too judgmental.
"Then it happened that as Jesus was reclining at the table in the house, behold, many tax collectors and sinners came and were dining with Jesus and His disciples. When the Pharisees saw this, they said to His disciples, "Why is your Teacher eating with the tax collectors and sinners?" But when Jesus heard this, He said, "It is not those who are healthy who need a physician, but those who are sick. But go and learn what this means: 'I desire compassion, and not sacrifice,' for I did not come to call the righteous, but sinners" (Matthew 9:10-13).
The question you need to ask yourself is whether or not attending the party is giving honor to someone because they are sinning. I would not attend the wedding of a homosexual couple getting married because the event is in honor of sin. But I have no problems with attending a work-related dinner given in honor of an employee who happens to be homosexual. In the latter case, the event doesn't honor the sin. "I wrote you in my letter not to associate with immoral people; I did not at all mean with the immoral people of this world, or with the covetous and swindlers, or with idolaters, for then you would have to go out of the world" (I Corinthians 5:9-10).
This changes if the person involved is a Christian who has returned to the ways of the world. "But actually, I wrote to you not to associate with any so-called brother if he is an immoral person, or covetous, or an idolater, or a reviler, or a drunkard, or a swindler -- not even to eat with such a one" (I Corinthians 5:11). Here the concern is not to show approval by indirectly showing that we accept the person even while sinning.
What other people think about us should not guide decisions about what is right or wrong. Morality is not determined by a consensus of people. The standards for our lives are set by God.