Hugh, what's the interview you mention...?
Yes, I think you are right about matters of the Tolkiens' marriage having been veiled a bit, and that's fine. I think the Tolkien family handled their normal, wholesome desire for privacy on one hand, and their realization that JRRT was of great interest to devoted fans and scholars on the other, with patience, tact, and generosity. I do wonder if Tolkien's diary/diaries will eventually be published, perhaps after those of us now in our sixties or older have died.
This account
J.R.R. Tolkien's diaries are unpublished diary entries written by J.R.R. Tolkien. The manuscripts are part of the Tolkien Papers at the Bodleian Library, a collection...
tolkiengateway.net
makes me wonder if Tolkien didn't keep a diary during some of the years we would most be interested in, or if the diary/diaries for those years have not been made available to any researchers but are retained by the family. You'll remember that somewhere in his diary Warnie, C. S. Lewis's brother, alludes to stresses in the Tolkiens' marriage. I can look that up later today.
It is easy for me to speculate and that's often not helpful. In some of my speculations about "sources and influences" I seem to have been wrong as further study has shown, and I had perhaps more to go on, on those occasions! But I have wondered if one of the complications in the friendship of Tolkien and Lewis was not just that Lewis married an American divorcee, but that there was so much happiness in their marriage, and that that might have contrasted a bit with the state of things in Tolkien's own marriage -- though he loved Edith faithfully and she him. I have pointed out this glimpse of the Lewis marriage before, written by "Tripods Trilogy" author John Christopher:
"The atmosphere was extraordinary; I had never been in the presence of two people sharing a gladness so pervasive as to seem almost palpable," etc. If Tolkien glimpsed this, it may have made him feel a bit sore -- not that he would have begrudged CSL his happiness.