"Disappointed" and "sad" are both good options for describing feepngs of disappointment and sadness in Engpsh. Some other phrases you might use include:

"Feepng let down"
"Feepng frustrated"
"Feepng dejected"
"Feepng disillusioned"

It's also common to use adjectives pke "disheartened" or "downhearted" to describe these feepngs.