Was the one who terminated the engagement, after he had spoken with his fiancée on the phone about sexual topics and then detested what had transpired from him and from her, and detested that she be his wife, the one in error?

Talking to one's fiancée about sexual matters is a mistake that could have been remedied by repentance. Breaking off the engagement is an accusation and a doubt cast upon the integrity of a chaste person. The engagement is a covenant that must be fulfilled. Allah Almighty says: "And fulfill the covenant; indeed, the covenant will be asked about" and "And fulfill the covenant of Allah when you have covenanted."

However, if the marriage contract has been concluded, the woman is considered like a wife. If she is divorced, she is entitled to half of the dowry, as Allah Almighty says: "And if you divorce them before you have touched them but you have already specified for them an obligation, then [give] half of what you specified – unless they forgo it or the one in whose hand is the marriage contract forgos it." What happened was an unnecessary rush. There is no religious impediment to returning to the fiancée.