Is what I did — distancing myself from someone I loved after making a covenant with God not to open my heart to anyone but my fiancé, and giving charity with the intention of good for him — correct? And is giving charity for his soul not forbidden? And is what I was told, that repeatedly seeing the name of my future husband in my life is an excess in supplication, true?

It is not permissible for males and females to discuss love and similar topics online, as it is a means to evil and a step of Shaytan. You must repent to Allah and occupy your time with what benefits you in your religious and worldly affairs, for if the self is not occupied with truth, it will be occupied with falsehood. If the man proposes to marry you, there is no objection to marrying him. It is permissible to give charity on his behalf or to dedicate the reward of charity to him. Asking Allah to reveal the name of your future husband is not an act of aggression, but it is a waste of effort and thought on something that yields no benefit.