My (24F) long-term friend (24F) asked everyone in the friend group to be in her wedding but me.

I want to start this off by saying that absolutely no one is obligated to ask ANYONE to be in their wedding, and I understand that completely, and that's not what this is about. I'm not angry at all and her wedding isn't about me, and I know that.
Just a quick backstory- I've had a childhood group of friends from around 2nd grade, one of them being my cousin. Her, my friend (we'll call her Mary), and I were kind of the 'three musketeers' if you will, and we tacked on a few more friends to the group through school. We've all been through a lot together, considering we've all been friends for nearly our entire lives.
Life happens, and we had a brief falling out a few years ago (I was dealing with really bad depression, she was in an emotionally taxing friendship with someone she's since cut out of her life) but never any major conflicts. Just didn't talk as much for a while. She had a child 6 months ago, and our lives are busy in different ways, but I still reach out to her. We've all been spending time together as a group lately again, and things felt like they were back to normal.
Anyway, she's getting married next year. Scrolling through facebook, I start seeing photos from friends in the group of their cards from her asking if they would be a bridesmaid- including one friend that's only been hanging around us for maybe two years. This really, really broke my heart. I started to really feel like maybe I was a bad friend, or there was something that I did along the way to make our friendship less valuable to her. I had planned to have her in my wedding in the future. It's going to be really hard seeing my group of friends be a part of her wedding while I sit and watch.
Has anyone dealt with something similar, and if so, how do I cope? I don't want it to effect my relationship with her, but i'm very hurt about it, and I don't know if I will feel the same about our friendship after this. And not only that, I feel selfish for being hurt in the first place. Part of me was really hoping she would address it, because I don't plan on speaking to her about it.
Any advice? I'm not sure how to get past this hurdle.
TL;DR- Friend of 15+ years who has a small circle of friends including me asked everyone but myself to be a bridesmaid- not angry, just very sad and unsure how to move forward.
EDIT: just to clarify, the falling out I had mentioned above was not exclusive to just me. The entire group was involved in that, mostly due to the situation with Mary