You must recognize that this relationship was more than a friendship. Just because you didn’t sleep together doesn’t mean you weren’t cheating. The two of you were carrying on a close, emotional relationship. His wife was correct to point out that the relationship was inappropriate for two people married to others. He was doing the right thing by ending the relationship and you should respect his decision to do so. It was the absolute correct action to take.
This relationship was dangerous to each of your respective marriages. You were attracted to one another and shared more than just class notes or study tips. You had developed a close bond. He was likely fulfilling a need that your husband is not able to at this time. You were probably fulfilling that same need for him.
In your mind, this relationship was not cheating because there was no sex. But in reality, this type of close relationship that the two of you had established, is more dangerous to a marriage than a strictly sexual affair. With the strictly sexual affair, there is usually only sex involved, no emotional ties. But with the type of relationship you and he had developed, you grew to care about each other. You were concerned with each other’s well-being. With a sex-only affair individuals share their bodies but in the type of relationship the two of you had, you shared your heart and mind. These later types of relationships, in which the two individuals grow to really care for one another, are the ones that usually lead to divorce.
You feel that he owns you a deeper explanation because you are hurt that he chose to end this relationship. But he ended it because it was wrong and it threatened his marriage. It threatened yours as well. Be glad that he chose this action because otherwise you might be facing a divorce. He did the right thing and you should respect this and move on.