IN a desperate bid to hold on to the love of her life, Robert Pattinson, Kristen Stewart is going for bust – with a boob job!

The “Twilight” couple is at a critical crossroads following the end of their vampire film series, and the 22-year-old actress is frightened that unless she does something radical, her 26-year-old boyfriend will kick her to the curb, say sources.

“Kristen is terrified that Rob IS going to leave her for someone else,” revealed an insider.

“She has always been insecure about her boobs, and she is totally convinced Rob would find it a

“Whenever they’re out together, she’s always on high alert to see which girls seem to capture his attention, and they’re al­ways girls with big boobs.

“She’s scared he may leave her for one of them. It’s an unhealthy obsession she can’t get out of her head.”

Kristen – who in the past com­plained she looks “like a boy” – isn’t the typical cosmetic breast surgery candidate, said a close source. “This is a girl whose makeup artist has to beg her to wear red lipstick and who prefers sneakers.

“But she’s desperate to hang on to Rob, and thinks a breast augmentation will do the trick.”