Instead of settling down with Biddy and what he has already, Pip decides to lurk around Estella. Why is Biddy not enough for Pip? What is it that a wise, educated and kind hearted person like Biddy lacks comparing to insulting Estella? Is it only good

Estella has been Pip's love for nearly his entire life, in his mind.  He cannot see the good in Biddy because he is so enamoured by Estella and his hope that she would, eventually, be his.  He thinks they have a "thing," and he keeps coming back for more of her treatment.  Ultimately, he may realize that Biddy is a good woman and a good fit for his needs, but as long as Estella gives him even the hint of a hope, he will not give up his desire for her.