Acceptance and trying to move forward

I've listened to all of the SoberAwkward podcasts and find them a wonderful tool in my sobriety kit. I am an alcoholic and have remained largely sober with a few blips for the last two years. Last night was one of those blips, I drank because I couldn't handle my broken heart. One of the main things I struggle with and can't find discussions about from other sober members, is how to live and move forward after my child has stopped all contact with me. My son left for University in September 2020, and took that opportunity to break free from me and my alcoholism. I know I have hurt him beyond words, I live with the shame and guilt running through my head as a narrative every day. I have tried to apologise through letters, I wrote heart-rending letters to him, but he won't respond. So many people on sober forums talk about how their lives have improved, they talk about improved relationships and better mental health - but I don't feel like I can move forward because of carrying this pain around with me. I am slowly accepting that I will never see my son again, it feels like a death, wrapped up with horrendous guilt. Christmas is a show, I'm putting on a Christmas face for my other two kids, but actually I'm heartbroken (they don't know I've fallen off the waggon a handful of times over the last two years, I've not drunk around them). What are we supposed to do when we have caused irreparable damage? Sobriety has to be better than drinking, but as long as I don't have my child I can't feel happy or whole. It makes everything painful, and makes sobriety feel unfair because it hasn't brought the rewards that so many of you talk about. Sorry for the heaviness of this post, I can't feel anything but pain at the moment.