What must I do, other than seeking forgiveness, after telling my fiancé “I worship you” in a moment of longing and passion, and then realizing and regretting it in terror?

What occurred from you was an unintentional mistake, and Allah Almighty accepts the repentance of those who repent. Allah Almighty says: "And there is no blame upon you for that in which you have erred, but [only for] what your hearts intended," and He says: "And He is the One who accepts repentance from His servants and pardons sins," and He says: "Say, "O My servants who have transgressed against themselves [by sinning], do not despair of the mercy of Allah. Indeed, Allah forgives all sins."

It is not permissible for you to call your fiancé unless it is out of extreme necessity, because you are still strangers to each other, and there is a fear of falling into being soft in speech. Allah Almighty says: "Then do not be soft in speech [to men], lest he in whose heart is disease should covet, but speak with appropriate words."

In addition to repentance and seeking forgiveness, give charity, for charity extinguishes sin. And be diligent in prayer, because "indeed, good deeds do away with evil deeds." And Abu Dawud, An-Nasa'i, and Ibn Majah narrated from Abu Bakr that the Messenger of Allah, peace and blessings be upon him, said: "There is no man who commits a sin, then rises and purifies himself, then prays, then seeks Allah's forgiveness, but he will be forgiven."

Abundance of good deeds is a reason for expiating evil deeds, and trust in Allah's promise to accept repentance.