The actor's world was blown apart after Kristen confessed to having an affair with her 'Snow White and the Huntsman' director Rupert Sanders and he moved out of the couple's Los Angeles home four weeks ago.
But the 22-year-old actress still believes their four-year relationship can be saved and in the notes she has been sending Robert she tells him she "made the biggest mistake of her life" and begs him to take her back.
A friend of Robert's told Life & Style Weekly magazine: "She's sent Rob handwritten notes - dozens of them - begging him to take her back. She says things like, 'I can't live without you. I love you. You are the one, and I made the biggest mistake of my life.' "
Kristen is so desperate to get back together with Robert, 26, she has even offered to go to couples therapy.
The pair - who play lovers Bella Swann and Edward Cullen in the 'Twilight: Saga' film franchise - are still on speaking terms which is giving screen starlet Kristen hope they could save their romance.
The source added: "Kristen has offered to do everything to win Rob's heart back - she even suggested couples therapy, which is a big change for her/ She said they could talk everything out with a third party.
She simply won't back down.
"She text-messages him all day, and Rob just sends one-word answers back."