OP, I’m having the exact same experience with a friend of mine. See my recent post in prayer intentions.
Watching what’s been happening to my friend over the last 20 months, I can tell you the advice here is spot on. I feel my friend was already being called by God, anyway, and I very much feel what he needed was someone to simply listen, hear who he is and all he’s done, and still show him the face of Christ–genuine acceptance and love regardless of what he’s done, someone to see all the good in him.
I’m not saying I set out with any great wisdom. I fell into this situation, am completely baffled by it, and feel God has guided me every step of the way, in feeling no judgment of him, in seeing the good in him. Everything that has happened is by the grace of God, by God calling him, and by him being at least open to faith and grace and God.
And over the past 18 months, this friend has decided on his own to stop going to swinger parties and bars, and picking up women. He’s started thinking more deeply about how his actions affect other people, and I haven’t said a word. Last Saturday, he offered to come to Perpetual Adoration with me, and Thursday night, he came into a church for the first time in 30 years. I have not asked him to do any of this.
Give your friend genuine acceptance. Be the face of Christ for him. Pray for him. Live your Catholic faith to the best of your ability, showing genuine humility, meekness, kindness, and so on, to others. Telling him he’s wrong or trying to sway him is almost certainly only going to make him dig in his heels and resist. He needs acceptance and to feel he’s loved where he is at the moment.