“The past is never dead,’’ as Faulkner memorably put it. “It’s not even past.’’ But the mutability of literary fashion continues to be regrettable. A new collection, The Luck of Friendship—The Letters of Tennessee Willams and James Laughlin (392 pages; Norton), reminds us of the importance of respecting the Muse (regardless of reviews), the seeming bygone virtues of literary mentorship, and the need to cast aside judgement to make way for love. Tactfully edited by Peggy Fox and Thomas Keith, Laughlin’s longtime associates at New Directions, the avant-garde publishing house he founded, it presents a little-seen side of the playwright. […]