I figured out the other mega-tie in with my pissed-off-ness.
Years ago, I was dating a guy who was in a serious accident. Unfortunately (no, the accident isn't the unfortunate part of this story), he had another girlfriend. He talked his mom into finally having me called to tell me about the accident and where they were, but when I got there, I wasn't supposed to hear anything from the doctors because I wasn't 'family.' That was the other girlfriend and her sisters' place.
Being excluded like I am feels the same way. Like I've done something wrong by thinking I should be included. Guess I misunderstood 'in sickness and in health.'