Eclipse #3

In the beginning of the next chapter in Eclipse, Jacob leaves to join the Cullens in the fight, but Bella cannot stand to see him leave. Edward leaves to bring him back so Bella can talk to him. While she is waiting, she keeps asking herself why she needs him so much and why she cannot just let him go.
"Why was that so hard? So very much more difficult than saying goodbye to my other friends, to Angela, to Mike? Why did that hurt? It wasn't right. That shouldn't be able to hurt me. I had what I wanted. I couldn't have them both, because Jacob could not be just my friend. It was time to give up wishing for that. How ridiculously greedy could any one person be?"p. 518
Bella wonders why it is so difficult for her to say goodbye to Jacob, more so that Angela or Mike or any of her other friends. She realizes that she isn't just thinking about the fight anymore, but she is thinking about being turned into a vampire and the fact that they will have to leave and she can't come back to Forks.
She also believes that she cannot be with Edward and still be friends with Jacob. Being in that situation would make not only her life harder, but also Edward and Jacob's. Knowing that Jacob loved her while she was in love with Edward would make her feel bad that she is making Jake miserable, and Edward would always be trying to comfort her and tell her that it isn't her fault.
This quote explains part of the reason why Bella has always had trouble with deciding between Edward and Jacob and keeping her life on track while still having both of them in her life.