There’s a hierarchy to sin, I believe.
Sexual sins between consenting adults with no cheating on a partner involved are not, as far as I can see, the worst of the sins.
Rather, sins more directly against charity, such as malicious gossiping about unverified rumors, holding grudges, cutting of communications with a close relative, lying to get a job, misleading customers so that they buy things that really are not right for them, and so on, are much worse sins, in my view.
Today, for political and commercial reasons (to win elections, to sell news programming), a great big deal is being made about gay sexual sins, while, at the same time, practically nothing is being said about the very widespread heterosexual sex between unmarried persons who are are dating in their late teens or 20s or 30s and so on.
I recommend: say nothing to your LGBT friends about their sins, and hope that they say nothing to you about your sins.
In our culture, there can be no doubt that LGBT people are very aware that most Christians/Catholics condemn their sexual lifestyle. Just be a good friend.
Seize upon this as a good occasion to really examine your self, and see all the sins of selfishness that you commit every day. We all do this, except for a few really saintly types.
Let this spur you on to more of the Virtue of Humility, and move more away from the Pharisee-like legalism and judgmentalism.
LGBT will become more open to Christ and His Church when they meet Christians/Catholics who are genuine, trustworthy, empathetic friends.
I think it always helps to remember this part of the Bible:
New International Version (NIV)
**The Parable of the Pharisee and the Tax Collector
To some who were confident of their own righteousness and looked down on everyone else, Jesus told this parable: “Two men went up to the temple to pray, one a Pharisee and the other a tax collector. The Pharisee stood by himself and prayed: ‘God, I thank you that I am not like other people—robbers, evildoers, adulterers—or even like this tax collector. I fast twice a week and give a tenth of all I get.’ “But the tax collector stood at a distance. He would not even look up to heaven, but beat his breast and said, ‘God, have mercy on me, a sinner.’ “I tell you that this man, rather than the other, went home justified before God. For all those who exalt themselves will be humbled, and those who humble themselves will be exalted.”
When in doubt, error on the side of being generous and accepting. That will do the most good.