They're meant to be together. Rosalie tells herself this on a daily basis.
Then she'll glance at Edward, Bella, and Nessie, and all of a sudden, she's not so sure.
She wants so badly to have the child Bella accidentally did, and she feels angry at the existence she's going to live because she cannot conceive.
She hates herself for bringing Emmett into the picture, and she wishes she could selflessly take back that selfish act. Even if that means she'd spend eternity alone.
Because meant to be is a tall order, and she's not convinced she can measure up.