"She doesn't know what a third wedding looks like," a source tells Us. "Anything lavish would be embarrassing."
Or not, considering Britney didn't exactly go lavish for the first two. For her quickly annulled Sin City aisle-walk with Alexander, she donned ripped jeans, a belly shirt and a trucker hat, while her backyard ceremony to K.Fed featured a menu of chicken fingers and cheeseburgers.
"Even though Britney has been married before, she looks at her wedding to Jason as her real wedding," explains the People confidant, who predicts the pair will tie the knot when she's wrapped work on "The X Factor."
As for recent pics of Spears without her engagement ring, the People mole has a perfectly plausible explanation, namely, she took it off for a photo shoot and Trawick, who was safeguarding it, forgot to give it back to her.
Britney, who continues to share custody of sons Sean Preston, 6, and Jayden James, 5, with Federline, began dating Jason in 2009. Keep clicking for a look back at their romance ...