For those who have been to the Kingdom Ministry School (KMS) or whatever it's called now, a teaching that may be little known to the R&F was discussed on the point of marital separation, not divorce.
The words "agreeable to dwelling" (old NWT) or "agreeable to staying" (rev. NWT) at 1 Cor. 7:12 have been applied as a principle that can legitimize martial separation. That is, on the surface, in the context of the apostle Paul's letter to the Corinthians, these words seem only to be talking about a Christian sister with an unbelieving husband. If he wants to remain married to the woman, then she should stay with her unbelieving husband. But the WTS takes this principle and applies it to other situations in martial life, some of which can lead to an acceptable separation, not—directly at any rate—to a divorce.
The thinking runs like this: if by one spouse's conduct he (or she) does things that can be viewed as non-agreeable to dwelling, then the wife (or husband) can separate from the mate. Such non-agreeable conduct can be certain kinds of physical abuse. I do not know the full history of this interpretation and application of 1 Cor. 7:12 in WTS history, but it may be that this is how it first came about, as a way to help those sisters who were being abused by their husbands. I remember it being stressed by the KMS instructor that such a separation does not free the sister from the marriage and enable her to divorce and remarry. It just sets up an acceptable—to the organization—separation which will not get the sister in trouble with the elders, CO, or GB.
I remember thinking to myself that if the unbelieving husband is a normal healthy horny guy, it won't take long for him to seek out sexual release somewhere else, and that would then give the sister the green light for divorce and remarriage. I also wondered how many R&F had so used this "arrangement" or "understanding" of 1 Cor. 7:21 to free themselves from a poor marriage selection.
Move down in time and I believe that this same principle has been further taken out Paul's original context and applied to Witness spouses whose mates become "apostates." This then is what Perry and blondie have referred to above. In other words, it's the supposed scriptural basis for a faithful Witness separating from his or her mate because of "absolute endangerment of one's spirituality," a spouse who questions the GB, the org, and all that.
I've been out for 20+ years now and do not keep up with the publications, so I do not know whether this supposed scriptural basis has been discussed in some publication open to the average publisher, or is still hidden away in the elder's handbook or in some BOE letter.
Perhaps someone who is still in and has access to the secret pubs can tell us the status in this "scriptural" interpretation for separation and/or its record for setting up handy divorces.