Need some help with boundaries

My father is someone I would describe as having narcissistic tendencies and being emotionally messy.” In conversations he tends to dump on those around him, conveying his disappointments with his life, his childhood wounds, his worries etc. To cope I generally keep my conversations with him really brief and about mundane topics to avoid being emotionally exhausted all the time. I’ve tried to explain this to him but he just doesn’t get it, and I’ve accepted that he’ll never change. Yesterday I had a longer conversation with him where I guess I allowed him to talk about some of these other things. He texted me later how appreciative he was about the phone call, that we hadn’t had a talk that good in a long time etc. But I just feel used and violated. He feels better because he dumped on me. And I’m mad at myself for not protecting myself better. At the same time I feel guilty that I attempt to censor the kind of topics he’s allowed to talk about. How do I create healthy boundaries to protect me from being his emotional dumping?