It is a not unfamiliar feeling, and there is limited ways to deal with it honestly. When someone doesn't include you in something that you would have like to be included in what can you honestly say or do. You can become a pest that always calls, I have done that before when my mental state was less controlled. It ruins friendships and even when you are included you still feel like a loser, you know that you had to work really hard at it. Or you can let it go, let a friendship drift off, and be back to not really enough social contact and try again.
The deal is that a friend I have through my meditation group was in a very close knit group of women studying with a Buddhist teacher for a few years. The out of state women came in 2 times a year generally for a long weekend retreat. I was so happy to be involved, it took a lot for me to get everything together with my time and my finances, and my kids were still at home. My mom even drove out last minute one time because the kids were behaving so badly that it was the only way that I could go for the weekend. I do spent time with this local friend, we went hiking a few weeks ago, we talk. I have been happy with the level of friendship. So I texted her this weekend because she traveled for her grandfather's funeral last weekend and it sounded emotional, I wanted to see how she was. I found out that another woman in the group was actually in Denver visiting and I didn't even know, much less get invited to anything like just tea. I have no idea about the details other then they went to the ballet, so this must have been planned.
How in the world do you say that you considered yourself part of the group when someone forgets you. I did once, I thought I was in a group of friends until I saw they went away for the weekend and posted on facebook. I brought it up and it went very badly. I recently talked to the dean at my school on a similar issue. I volunteered and did mindfulness for 3 years in classrooms, they liked it so much they created a mindfulness room and hired a coach. They didn't even introduce me although the dean I talked to assured me they told her how great the work I had done was. It is done, what is there to be said. I am glad I said something but I don't really feel better.
Anyway my local friend wants to meet at Starbucks before our meditation group tomorrow night, so I need to see what I want to do.