I won’t comment on what is/isn’t sinful in his situation (having a boyfriend can’t be in the slightest, though perhaps expressing their mutual love in particular ways is, for the Church at any rate). But I don’t think there’s actually an inherent contradiction in being homosexual of itself, and in being a faithful Catholic.
First of all, there is undoubtedly sin in his life (there is, frankly, in everyone’s - it’s just fairly obvious in what way for him!). But that doesn’t mean he can’t be entirely faithful to Church teaching in every other respect, and he’s only drawn towards sin in this area because of whom he is naturally built to fall in love with.
The Church’s - and indeed all of western society’s - rather…awkward…obsession with sex (in any kind of context) I think rather gives the impression that how one expresses sexual desire is the ONLY or HIGHEST arbiter of one’s personal identity. That’s clearly rubbish. Your friend is a faithful Catholic man who happens to be gay - rather than a gay man who is also trying (best he can) to be a faithful Roman Catholic.
One of my closest friends, from my church, is also homosexual, and in a (platonic, as far as I can tell) relationship with another woman. Just because she’s gay, that doesn’t mean automatically she disagrees with Church teaching on the matter, or that she desires to disobey it. She is just as faithfully - even stunningly conservative - Catholic as the next woman, who happens to be in love with another woman. I suspect it’s a similar case to this man’s.
I don’t know how he must feel in his heart, about these two aspects to his life each of which must bring him great joy - because there’s frankly inherent conflict between the two. In one sense his situation maybe is “worse” because he will unequivocally know what he is doing is sinful; on the other hand I think there is something to greatly celebrate in someone who is at peace (?) with his sexuality but has not felt driven from the Church as a result.
I suppose it’s very similar to all those millions of Catholics who use contraception (there are WAY too many 2 or 3-child ‘good Catholic’ families for everyone to just be practicing NFP!). If one can square it with one’s conscience then that doesn’t make it ok but a compromise between accepting the nurturing love of Christ and the love of another human being sometimes has to be made somewhere, sometimes. That doesn’t necessarily stop is being sinful but I’m pretty sure that God does, in fact, understand.
To go back to the original issue, it’s one area where the Bible is rather unequivocal on the matter. But were this man known to me, I would not talk to him or pray for him that his life might be changed, but only that his soul is in this life, and shall always be (especially this Sunday), at peace.