D.W.
McK4's experience is pretty much the same as ours.
Our son has only stayed in his bed a few times since moving into it almost 18 months ago. Every night, he finds his way into our bedroom and into our bed. My Mother-in-Law suggested putting a sleeping bag in our room as his place of haven when he comes into our room.
We don't know what prompted his fear of being in his room, but we've not been able to abate it either. So, for now, the easiest path is to let him come in when he's ready so we can all get some decent sleep.