disappointment
憮 centers on a feeling of letdown or dissatisfaction: the emotional state of disappointment when expectations are not met.
憮 combines the heart radical 忄 with 無, which likely contributes the sound ブ and may relate to the idea of lacking or not having, fitting the sense of disappointed expectation.
The heart radical 忄 beside 無 (nothing) suggests a heart feeling empty or let down: disappointment.
For ブ, imagine a disappointed boo from a crowd when expectations fall flat: boo -> ブ, and the heart sinks.
disappointed; dejected; disheartened; glum; astonished; dumbfounded