Why?

I lost a friend to God yesterday..and the only things i see around are lacunae.Why is it that we take people so forgranted that we forget someday we will lose them permanently?would never be able to call them up,meet them,laugh with them,fight with them...never ever?
And most importantly,why do these questions arise in our mind only when the person is gone..either from this world ..or from our lives?
If some people means anything to us..lets keep in touch..lets keep reminding them that we are always around..we would stand the test of time for them...that we love them.