My recently widowed sister wants me to confront her husband’s unfaithful past. What to do?

‘If others bear witness to the things that hurt us, our feelings aren’t the only monument, so we can let the feelings go,’ writes advice columnist Eleanor Gordon-Smith. Painting: Slumber Divine (Sketch for a Panel) by Victor Borisov-Musatov. Photograph: Artepics/Alamy

Help! My recently widowed sister wants me to confront her past, for her. My sister, 63, was with her husband, 67, since she was 16 (they got married in their 20s). As sometimes happens to widows/widowers, she is now questioning their relationship. He was unfaithful to her several times, but she chose to stay (they have three grown children.)

One of his possible indiscretions was with a childhood friend of mine, with whom I’ve had sporadic contact over the years. Recently the friend contacted me, out of blue, to have dinner together. Neither my sister nor I know if anything actually happened between them, and her husband always denied it. This was in the 1980s.