It would take a certain personality to believe that a random international internet stranger who is much younger, very good looking, flirty and generous with flattery would develop an instant adoration and sexual attraction for someone they’ve never met.

I think there might be a subgroup of victims who fall for it out of loneliness, even if they may suspect something is not right they continue because it’s respite from their loneliness. But sounds like your neighbour is not in that group, and just has a lot of ego.