If you were blackmailing someone in your dream, it shows the lack of trusting yourself. As we know the blackmailing is something that is illegal and causes negative consequences, which foretells that your behavior is not the way it supposed to be. When the dreamer sees himself being blackmailed by the others, it shows that you are reaching out for help. You do not trust yourself, have no confidence with your own personality.
Read more about dreaming of Blackmail in other dream meanings interpretations.