Friends hangout without me every weekend

I’m in a friend group of three other people. My friends have been hanging out together every Saturday. I have known for a few months, and they’re not secretive of it, they plan hangouts in our gc right in front of me. When I found out about the hangouts I asked if I could join, I was told that “it’s a special thing between families”. I don’t understand what that means. Why don’t they think to ever invite me? We’ve been friends for 2 years now but I still feel like an outsider because they’ve known each other longer. I feel upset but when I think about it from their perspectives I’m a boring person that doesn’t even cross their minds. I don’t come from an easy family, my mom is abusive and my friends and their parents know and I think people want to keep distance with me because of my mom. I would like to confront my friends but I’m not sure how to word it, maybe it’s not worth bringing up because it will be awkward? Sometimes I feel like we’re really close and having fun and then I’m smacked back to reality with things like this. I’ve told them that I really like hanging out I really don’t get why they don’t invite me, I barely see them at all. I try to be a good friend, I put a lot of effort, I don’t understand what I’m doing wrong