Let down.
The feeling of disappointment is such hollowness your heart drops a million feet below sea level you run out of breath and let your head drop towards the ground you desperately wish you could dig up and hide in where noone in the world can touch you it feels like someone just punched you in the gut and you're left lying there, left behind, let down, alone and disappointed you try to explain it to someone but rarely do you ever find the words to describe exactly just how you feel and that person will never understand. You try, and you try to make him understand just how painful it is, but you'll never succeed, not ever.
And all you can do is,
give up.