Complex sentence: Pip fears Estella could never marry a commoner like him, but a man comes in bearing an offer for Pip; an anonymous benefactor has agreed to pay for Pip to go to London and learn how to become a gentleman.
Split into simpler sentences: Pip fears Estella could never marry a commoner like him. However an offer comes for Pip from an anonymous benefactor to move to London and learn how to become a gentleman.