Dishearteningly means in a way that makes people lose hope, or as a comment on a whole fact: sadly, this took hope away. You often meet it at the front of a sentence. Dishearteningly, only three people came. It is rather written and a little heavy. In speech people more often say sadly, disappointingly, or it was so disappointing that… Though actually, it does not mean in a cruel way. A kind person can tell you something dishearteningly true. It is an adverb, so it tells you how, or it judges the situation; it is not a word for how you feel inside. To name your own feeling, say I am disheartened.