The story I've devised for my char is that he started searching for certain answers in "forbidden lore" (to quote the PHB), struck a pact with a Fiend, but after a while, realised the Fiend couldn't give him what he was looking for. So, he started looking elsewhere (stopped taking levels in Warlock), which raises a question: How can I RP "breaking off" from my Patron?
The ideal answer will provide precedents from the DND universe (either lore/story or class/mechanics). More generally, I'm looking for something along the lines of this answer, especially the quoted section, where the character justifies/describes why she is not her class.
The relevance of that answer has to do with the player successfully detaching the character story/background from the class. I'm looking to achieve a similar detachment: keep my character developing through a varied path without feeling like I've left a gaping hole in his story.