Disappointment
Despair
noun, verbal noun
There is fault in your hope. It breaks, and everything falls apart. You feel massive disappointment and despair.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
失望を味わう
to experience a letdown
失望をする
to be disappointed
失望を感じる
to feel disappointment, to feel despair
君には失望したよ。
I'm disappointed in you.
この映画を見た後は、何とも言えない失望感を感じました。
After watching this movie, I felt a sense of indescribable dismay.
期待するからこそ、期待通りにいかない時に失望しちゃうんだよ。最初から期待しなければ失望もしないさ。
Disappointment comes when things don't go as expected, precisely because you had expectations. If you don't expect anything from the beginning, you won't be disappointed either.