What is the ruling of the Sharia on dealing with a fiancée who is attached to her cousin – who is four years older than her – to the extent of going out with him and talking on the phone, and she refuses to cut off this relationship after marriage, knowing that her family sees them as like siblings, and should the suitor be patient until the marriage is completed or should he break off the engagement now?

If your fiancée is accompanied by her female cousin's son, whether an adult or a teenager, and they go out together alone, this is an obvious evil that cannot be condoned, because he is a mahram to her, even if he grew up with her. Explain to her the ruling of Islamic law on this matter. If she repents and adheres to the limits of Allah, then that is good. But if she insists on her negligence, then leave her and seek someone else from among the righteous women.