How do you overcome emotional blackmail?

Weigh up the pros and cons of what would happen if the truth came out anyway (as it usually does eventually) and if you can live with that then get everything out in the open, as hard as it will be at the time. Also when you do that, let the person you've told that you have not told them to hurt them, you wanted to come out and be honest about it anyway, especially as you know that someone else was going to tell them anyway and you would rather they heard it first from you. Either that or pay up and keep stchum!