Is it permissible to shake hands with one's fiancé, and how can one convince others of the reprehensibility of shaking hands if it is not explicitly forbidden by text?

It is permissible to greet an unmarriageable woman (ajnabiyyah) if there is no fear of temptation (fitna) and no suspicion (reeba) arises, such as a suitor greeting his fiancée, provided they are not in seclusion, as he is still a stranger to her. It is not permissible for a man to shake hands with an unmarriageable woman, based on the Prophet's (peace and blessings be upon him) saying, "Indeed, I do not shake hands with women," and his saying, "For one of you to be stabbed in the head with an iron needle is better than for him to touch a woman who is not lawful for him." As for a man shaking hands with his maharim (unmarriageable kin), Imam Ahmad ibn Hanbal disliked it and was strict concerning it. Perhaps refraining from it is more preferable in this day and age due to the prevalence of corruption and the arousal of desires.