From Longman Dictionary of Contemporary Englishfizzle out phrasal verb informalSTOP HAPPENINGto gradually stop happening, especially because people become less interested Their romance just fizzled out. → fizzle→ See Verb table
Examples from the Corpus
fizzle out• Their romance fizzled out after a few months.• The movie made a great start, but the action seemed to fizzle out halfway through. 