Happiness vs sadness

Him: If I left you one day, what will you do?
NQ: Hmm...I'll continue to live....I still have my job and my family. What about you?
Him: Same. Love is just a part of my life, you are not everything to me. I still have my family, career, dream and interest. But, I am glad to hear your answer because you always make me worry that you will not survive alone without me.
NQ: :)

We can't expect each other to die on the same day, at the same hour, same minute and same second. Hence, the one who is left behind will have to bear the pain. God is fair. It grants us emotion. When someone treats us nice, we feel sweet. When someone lets us down, we feel sad. So, if we get to experience the happiness, then we should expect the sadness too. When we are happy, we never ask why we deserve the happiness. Then, when we are down, why do we ask why?