Most Helpful Guy
Please don't. Out of hatred only comes more hatred, its infectious. Its better if you just leave and move on. He can't stop you from leaving, only you can. There is no need to be cruel, just be very firm about your decision and make clear you won't be changing your mind. The heartbreak he will suffer from that will be punishment enough.
Most Helpful Girl
Rather than take revenge, just leave him. The only person stopping you from leaving is you. You're your own person and you've made up your mind so leave him and don't let him control you.