It is not permissible for a fiancé to be alone with his fiancée

It is not permissible for a man to be alone with a woman who is not his mahram, because that affords temptation to do immoral and evil actions. The Prophet (peace and blessings of Allah be upon him) said: “No man is alone with a (non-mahram) woman but the Shaytaan is the third one present.” It is permitted to look at her when one has the intention of marriage, without being alone with her and in the presence of her father, brother, mother, etc., and looking at that which ordinarily appears of her, such as her face, hair, hands and feet. This is what is indicated by the Sunnah, so long as one is also free from the risk of fitnah (temptation).