
As I understand that the OP’s brother is reading this thread too, I’ll just address this straight to him.
I’ve been trying to think how I’d want my son to raise the issue of his sexuality with me if he was gay. I’m struggling because we don’t have a son (

we’re hoping, but it’s work in progress!) but I do have friends who were brought up Catholic and are gay and living with partners.
What would matter most to me is that my son could be honest with me. As a Catholic, I have all those beliefs about mortal sin and Hell and the thought of my baby (no matter how old he is) ending up there would be an awful thing to contemplate in itself, without thinking he was living his life on Earth hiding a secret from me and agonizing over my reaction.
I would appreciate being told in private, without the boyfriend present and with some prior warning that you had something pretty big to tell me. I would also appreciate your understanding that the news will take a while to sink in and accept that for a while, I may be lost for words. I might scream and rave, or I might be left speechless! I might say things that hurt you and me because I am in shock. I would like you to know that I still love you and we are still family. As a Catholic, above all, I believe you are created by God and God makes everyone for a purpose, so I still believe you have lots to bring to the family and the world regardless of your sexuality.
I would be thankful if you told me that while you haven’t embraced the Catholic Faith in adult life, you have learned enough from your upbringing and education to be a compassionate and kind human being, who knows right from wrong. I’d like you to talk openly and calmly (one day - maybe not the day you break the news) about the Catholic Church’s teaching on sex outside marriage and see that as a Catholic, I love the sinner and hate the sin: I do not advocate discrimination or hatred towards gay people.
I’d also like you to respect my beliefs and accept that you and your boyfriend would not be sharing a bed under my roof if you came to stay. If you felt you’d rather stay elsewhere, I’d respect that. I would say exactly the same if you were sleeping with a woman outside marriage.
I can’t speak for your parents, but for me, even though I might never accept that same-sex relations are not disordered, I would still see you as a wonderful human being and as my son. I would hope with all my heart that you could still accept me as your mother.