When you work for bigger causes, you come accross points where you are too much strained and burned out.
True that... And in those times we need to find deep within ourselves our purpose--the reason why we do what we do.
I am sure those who work for benefiting others are those who enjoy doing so. If they stop doing this, they would feel empty.
Spot on.
So, you wouldn't feel happiness if you stop being altruistic.
The time of disappointment shall pass. More powers to you