After someone hurts you, you're not the same anymore. Life is a constant flow of changing circumstances. Some good, some bad. Each experience molds you. Use these experiences to develop yourself into the loving person you are and will continue to be
The beauty about Ursula is that she held up her part of the bargain, gave Ariel 3 days to kiss the Prince. Nowhere did Ursula say she could not interfere. It reflects how real life contracts work... Student loans for example.