Talking about leaving the lights on. ..my house used to resemble Blackpool illuminations and that was to comfort the two adult women in the house

I really don't get all this fear of the dark nonsense. ..now I can sleep comfortably in my bed in total darkness with both eyes closed. ..bliss! !!!
My boys, like me didn't have a problem with the dark or sleeping alone in their own rooms.
Sympathise with your situation. .must be so hard. ..sleep deprivation is tough.
The idea of keeping him up until he falls asleep is a terrible idea. .kids need routine .especially going to bed at a specific time routine.
This is the sort of thing you see a lot doing in the Philippines. ..you'll be making rods for your own backs. As said before. .tough love
Mine were in their own rooms at 12 weeks. ...no adjustment problems, no fear of the dark.