I see this as another opportunity to work through such an issue as being left out. You can access the listing of the Social Groups within your Messages (PM page) on the left hand side, down in the column. Click on that and you'll see the listing.

There will always be places or access to which one is denied, whether a child or an adult. That's part of life. Try not to take it personally, then, fill that void with places you can go!