Do you realize how messy her life was and is?

1. she cheated on her husband with his best friend
2. she tried to repair relationships both with Derek and Mark; Mark wanted Addison to be with him, but she didn't.
3. she slept with an intern [Karev] and hoped it could be something more
4. she moved to LA and wanted to change her life so she didn't want to start seeing Pete because he was a good time guy
5. she cheated on her boyfriend Kevin with Wyatt
6. she fell in love with Noah, her patient's husband
7. she slept with Mark, Lexie's boyfriend; Addison wanted Mark to be with her, but he didn't
8. she fell in love with Sam, her best friend's ex-husband
9. she lives with Pete, who kind of belongs to Violet.

She wasted her chances - with Mark (GA S03), maybe Pete (PP S01), with Sam (PP S03) and I'm afraid that Violet will took her Pete now.

I totally agree with decision that Addison and Pete made, to be together, to move on, to build their happiness, to become a family maybe. IT'S AN ADULT THING.