Sosoconfused, others have already made the point that your friend may not be leveling with you. People lie for many reasons, and I think that there is a chance that you are not being told the truth.
I don't know your friend, but I have sat on many judicial committees and here are some of my observations: If what your friend says is true, this judicial committee rendered a stunningly egregious verdict against this couple's marriage. It is completely indefensible, and is unsupported by anything in the scriptures, the WTS literature, or by common sense. It is impossible to commit adultery if you're not married, and adultery is the only grounds for gaining a scriptural divorce (in Matthew Jesus said it was "fornication" but JWs understand this to mean pornea with someone other than your mate, so for this to apply your friend would have had to be married to her at the time).
So here's how it should and would normally go down, even in the unfair world of JW judicial committees: The wife confesses to the husband and then they go together to a judicial committee. If the husband is not put off by this (and why should he be--they didn't even know one another at the time), the sister is counseled and perhaps privately reproved, but likely as not, she may get off with just counseling and perhaps losing her privilege of pioneering for a bit. If the husband is repulsed by the conduct of his wife, that would not change what happens to her as far as the congregation is concerned. She is no more culpable if he is put off by her actions than if he accepts them. If he decides to initiate a divorce, the judicial committee would inform him that he may do so, but that he would not be scripturally free to remarry. There is no indication in Christianity that a bride has to be "pure". That is 3500 year old Israelite garbage that was worthless back then and even less applicable today. If this situation had come up on just about any committee I've served on, the elders would have counseled the couple to stay together, and in fact, no committee is ever supposed to counsel a person toward a divorce. Even in the case of adultery, the innocent mate has a right to forgive if he wants to.
There are plenty of nutty elders out there who, on their own, might be capable of rendering such a moronic decision as you describe. But that's why there are at least 3 elders on a judicial committee. The idea is that if the committee goes completely off the rails, at least one of them will yank the others back on track. My experience is that elders and judicial committees don't hesitate to call the service department when they have an issue that is complex or that might spawn litigation. I have sat on a number of committees that did this. There is no way the service department would have agreed to their decision.
So to my thinking, the situation your friend described to you would almost have to be a conspiracy between him and at least three elders. I suppose that is possible, but it is unlikely. This sort of thing would expose the congregation and the individual elders to a civil lawsuit. The issue used to be called Alienation of Affections, but I understand that is no longer used in most states. I would think there is some similar basis for suit that has taken its place. Perhaps some of the lawyers on our forum can answer that.