Jacob lets Bella in on a few secrets of the werewolf pack. His best friend Quil has recently become a werewolf too. Quil loves it and so do all the others, with the exception of him and Sam.
When Jacob mentions that you don't age as a werewolf, Bella throws a full-scale hissy fit: "I get older every stinking day. Where's the justice?" (5.76). It's a sore point, obviously.
Bella learns that Sam, the leader of the werewolf pack, was in love with Leah Clearwater before he "imprinted" (read: "love at first sight" for werewolves) on Leah's cousin Emily. He broke Leah's heart, but he had no choice. Imprinting is a genetic quirk of werewolf nature.
When Bella asks Jacob is he has "imprinted" yet, he says no. He further explains that one thing all werewolves struggle with is that they can't keep their thoughts private from the pack.
On the subject of thoughts, Bella asks Jacob what he did to Edward during their confrontation at school. He admits that he reminded Edward, through his thoughts, of the day Sam found Bella in the woods, a bundle of misery. Bella gets mad at him:
"I don't care who's a vampire and who's a werewolf… You are Jacob, and he is Edward… And nothing else matters." (5.175)