Is my description of my husband's female colleague as "bad," "treacherous," and a "hussy" considered backbiting (gheebah) and name-calling (tanabuz bil alqab), especially given that she initiated the flirtatious correspondence that led to the development of the illicit relationship between her and my husband?

The Alawites hold beliefs that take their adherent outside the fold of Islam. Scholars have differed on the ruling concerning the backbiting of a disbeliever, and it is better for a Muslim to refrain from such. The relationship between your husband and this woman—if proven—is sinful, especially since she is married. His desire to guide her does not justify this relationship. He must repent and sever his ties with her immediately. The claim of addiction and gradualism is a psychological trick and a satanic whispering.