I felt this way a lot, too-- though with e-mails because she didn't allow texting. For me, it's because she brought up so much RAGE in me, and it felt so unfair that my night was ruined thinking about how awful she made me feel while she was off having some lovely evening with her wonderful, successful, wealthy-beyond-belief children.

But even if she wasn't the target of my actual anger, as you say, she was the only person in my life I could actually express my unfiltered rage to (which was one of the reasons I had to terminate. The rage was getting to the point where it was so hard to quiet that it was taking a huge toll on my physical health).

Once I wanted to write an angry e-mail, but all I wrote was "When I come in next week, please ask me if I'm still angry." She did. I was. I didn't have to put terrible things in writing, but I was able to be a teeny bit aggressive via e-mail and then a lot aggressive in person.