Luke 15: 1-7 Parable of the Lost Sheep
Then drew near unto him all the publicans and sinners for to hear him.
And the Pharisees and scribes murmured, saying, This man receiveth sinners, and eateth with them.
And he spake this parable unto them, saying,
What man of you, having an hundred sheep, if he lose one of them, doth not leave the ninety and nine in the wilderness, and go after that which is lost, until he find it?
And when he hath found it, he layeth it on his shoulders, rejoicing.
And when he cometh home, he calleth together his friends and neighbours, saying unto them, Rejoice with me; for I have found my sheep which was lost.
I say unto you, that likewise joy shall be in heaven over one sinner that repenteth, more than over ninety and nine just persons, which need no repentance.
In this parable, Jesus teaches us that we are to search for the lost souls. The 99% of on the righteous path are fine and need no assistance. But abandoning the 1% is simply not an option. We need follow Christ's example by seeking out the sinners and help them come back to the flock. To do less means we are also lost. To do less is un-Christian.
You should remain friends with this person, but you should not condone his homosexual lifestyle.