Is it just me or do people truly not understand me?

I've had these persons for whom I thought I was understood by; I just thought they "get" me, that they know what stresses and hurts me most deeply. To an extent, I thought all people understood what hurts me beneath my "all-is-good, let's-be-happy" acting. Yet, they seem to have fallen for the acting. They actually seem to have started to believe that these things do not hurt me, so they proceed conducting themselves accordingly.

Is it just me? Is this a common situation, or a somewhat interesting thing occurring only to myself?

If I truly am not understood, should I quit the acting? What do other people do?

I feel this question shouldn't be asked by a 21-year old (who ought to know these things), but I'm truly lost.