This routine was really wearing me out, but, I didn't want to fall short of my parents' expectations.

fall 是动词，意思是"落下、下降"。 short 是形容词，意思是"短的、不足的"。 of 是介词，表示"关于、属于"。 fall short of 是一个固定短语，意思是"未能达到(标准或期望)"，在这里指"辜负(期望)"。