Do something while sniffling, sobbing, or generally feeling blue, and you do it forlornly. When you just miss the ice cream truck, all you can do is watch forlornly as it drives away.
It may break your heart to leave your dog in the morning when you go to school, especially if she gazes forlornly after you through the window. Anything done forlornly is full of regret, loneliness, and even hopelessness. This word derives from an Old English word meaning "to abandon or lose."