Given what he is a person i doubt he was ever genuinely friendly, i suspect something more akin to pretend to be nice and friendly to get close to the object of his desire.
He sets his targets on her because she most likely was the prettiest, most desired girl in school and getting her would make him the baddest MOFO, her constant denials just made him more obssessed.
With him getting older and learning he could get what he wants by flexing his power better than with his "charms" his approach changed.
With that said the fact that he still thinks she's playing hard to get is unbelievable.
As shown in this post by
valbitterb ...
How deep inside his own fantasy can a person be?