I misinterpreted what you wrote. I don't know the answer but I can guess. And I can't speak for everyone - we're not a homogeneous group that thinksalike. I can only share my own experience.
As much as we're in love with our LGFs, life happens. As we're not openly in a relationship, it fades away when LGF moves away, for example.
Or she falls in love with another boy and you fade away. In a teenage turmoil it's not uncommon for people to "break up" and find someone new.
And there's also the "fact" that every adult who loved you as a child is a creep and you should hate him. A lie that has been repeated a thousand times becomes the truth.
Also, some pedophiles grow out of their affection as the LG grows older.