It's tempting to shortchange someone who treated you poorly and doesn't deserve to be repaid. They didn't keep their word, so why should you? Unfortunately, the only person you'd be cheating is yourself. It's unfair being the injured party who has to recompense the person who wronged you, but do it. You don't want to be around this toxic energy any longer than you have to be. It's like wanting to retaliate against a driver who rides your tail or runs a red light. This person is an accident waiting to happen, and the sooner you're as far away from them as possible, the better.