Not entirely sure what you mean about talking to Jer first being the trigger? The scene will be available to find so long as you don't tell Will to leave Duncan alone. Are you possibly loading an old save or something?
i was loading saves, as i was looking to make sure i hadnt missed anything and while doing so i probablly forgot i had told will to leave duncan be tho i did notice if i had talked to will and duncan before it gave me a dif ending to the fatal vore scene
