I think you just have to guess with the dots lol
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Yeah I agree that he must have taken his own life, but it is more the reasoning behind it that confuses me. It suggests that he doesn't even remember Annie (or anyone else) which is why he is excluded from the curse, so he might not remember the whole situation with Annie in the Chapel, and therefore not remember his guilt. The invitation from Rupert Galley suggests that John was having a particularly rough time following his divorce which is what led me to think that maybe his death was due to that.
It completely went over my head that the audio going on for so long meant that it took a long time for him to die - he must have still been alive after jumping from the attic but bled out (or succumbed to his injuries) at the entrance where he landed.