Here's a very tentative hypothesis: I get angry when things don't work right, when systems break down. But when people let me down, that's already in the equation. I expect to be forgotten or pushed to the side some of the time. It's not like there's any friend who never comes through for me; everyone does, in their measure. I've learned, however, that those measures are limited—that if I want to really be able to count on something, I have to make it work myself. When I can't do that, that's when I get angry.
In sum: I expect relying on others to eventually be futile, but I expect that I can make things work. That's pretty screwed up in multiple directions.
So today I was tired and gave up after a phone call. I'd rather let it go than to continue to bang my head against the wall and ruin my chance at a little rest. There'll be time to be angry later, I suppose, if I need to be. I'm not denying that there's disappointment and hurt; I just don't want to make it bigger than it is.
marm gently suggested that my expectations of friendship may be too low. She's right—it's not supposed to be this way. Yet it is this way, and perhaps it's necessary to accept that.
I'm more bothered and hurt now that I've written. That wasn't such a good idea, perhaps.