Cause and effect (causa efecto)
Because (porque) / as (ya que/como) / since (como/ya que)
Como no has venido no te he visto (presente perfecto = have/has + participio)
As/since you have not come I have not seen you
Como no viniste no te vi (pasado simple = -ed/2ª columna verbos irregulares – did=auxiliar)
As/since you did not come I did not see you
Te he visto porque has venido
I have seen you because you have come