We must remember that authors create fictional personae in their works. The narrators of Lewis' books are created by him but are not "him" in the regular sense of the word.
Modern critics talk about "the death of the author" and "the biographical fallacy." Since a text exists independently of its author and is not begotten like a son by the father or created as if by God (says Roland Bathes) it is wrong to judge a work of literature based on an understanding of a writer's personal life. Works of literature arise out of language and other works of literature, not out of the author's personal life and it is fallacious to interpret them with biography as one's primary source of judgment.
I agree with this to a large degree, though I think it needs to be modified somewhat. Biography does come into play to an extent. But the intellectual influences and literary influences are much more important and have much more bearing on a book than our understanding of an author's life.
So the myths and the similar books that influenced Till We Have Faces are infinitely more important to correctly interpreting the text than our ideas of whether Lewis had a close relationship with Joy Davidman or what was his attitude on women.