Dear Peter,
You were right, Uncle Bobby doesn’t exist. Matt and Katherine agree: psychological coping projection.
- Old Mike says at the beginning and the end that truth is in the teller and history is how you tell it.
- The stepfather going to jail and Bobby leaving happens at the same time, because Mike didn’t need him anymore.
- At the end, old Mike says “that’s how I remember it.”
It isn’t like The Sixth Sense, they don’t give you context clues, but after watching it I’m pretty sure that Bobby is meant to be fictitious.