My fiancé(e) has been found cheating or has changed. What should I do?

You have the right to end the engagement; this counts as a valid reason, and it is better that it happens before the contract.
An engagement is a period of assessment, and early signs such as cheating, harshness, excessive control, lying or neglecting prayer are serious warnings. Do not assume marriage will change them. Discuss it with your wali and family, gather the facts, and decide calmly after istikharah. If you end it because of his or her wrongdoing, you are not regarded as breaking a promise without cause, and the question of gifts and expenses can be negotiated or taken to the Syariah Court. Do not expose their faults on social media. If there are threats or harassment, report them to the authorities. See counselling.