One of the issues with discussing homosexuallity in our culture is that the LGBT (which is a political label) have indoctrinated homosexuals to be excessive sensitive to anyone who refuses to jump on board the “gay lifestyle” choo-choo train of tolerance (even before my conversion, I was still uncomfortable with LGBT for this reason).
They don’t want rational discussion, and instead they continuously create a smokescreen of blant assertion and bad arguments and strong feelings (not to deny their feelings aren’t completely justified: despite my disagreements with homosexuallity I know it is a harsh thing to bear) that can be used to dismiss any sort of moral standard at all.
In fact, the ultimate standard homosexuals who have been lost in the fog judge by is the acceptance of the homosexual lifestyle or not. They look at a product and think: does this company accept gays, or at least is neutral on the topic? If there is any hint of “homophobia,” than they reject it wholeheartedly. That’s why they can never accept Church teaching; they judge not by God’s standards, but by LGBT ones. LGBT is right, and anyone who dissents is wrong and must be reformed! St. Thomas says that Lust distorts the mind and rational thinking: those on the LGBT train have been mentally poisoned by the exhaust.
You must understand that this is the sort of mindset many homosexuals breath in from being on that train. They judge arguments not on correct premisses and logic, but on conformity to LGBT. In other words, LGTB is only tolerant of itself. Don’t let the speaches about tolerance fool you.
Now, I know many homosexuals are sane enough not to buy into this fully, but this mindset seems to be unconscious in most minds regardless. I tell you because this is a warning: homosexuals might not being willing, to be openminded to the possibility of them being wrong. At least they might proclaim a moral relativism to dismiss Church teaching. In that case I don’t know if it is worth discussing the topic. That’s your call: I’ve never been in your shoes.
I guess the key point I’ve been impliedly hitting is that LGBT homosexuals are nihilists, at least in regard to sex. They don’t believe in objective meaning. If you can convince them that sex has a meaning, a purpose, and that if sex doesn’t have a meaning than how could anything else, you might be able to save their soul.
Of course, prayer is always the best thing I just want you to better understand the sentiments and state of mind of the train wreck of LGBT. One wrong move and your friend will hate you (especially since he trusts you enough to tell you this), and he will build a (unfounded) prejudice against Church teaching that She is irrationally intolerant of gays, which just makes the situation worse for them.