Don’t take it too personally. Sure, at the moment it may seem as though they are excluding you, but many sources can come into play that may have given them reason to not ask (I.E., they thought you were busy, didn’t like where they went, had private matters to discuss, etc). Also, don’t completely drop them as friends for this one isolated incident, unless there have been other occurrences where they have mistreated you or otherwise been rude.
