"Kristen wrote a long letter explaining her love to Rob. She feels that even if he can't forgive her, he should know that she is closer to him than anyone else could ever be," showbizspy.com quoted a source as saying.
The couple recently agreed to a trial separation.
Meanwhile, Stewart, 22, is said to be angry that Robert Pattinson isn't giving her enough attention while he films “The Rover” in Australia.
"She was devastated when Rob suggested they go on a trial separation, and Kristen Stewart has been eager to visit him, but now she is getting seriously angry at Rob because he is so bad at keeping in contact," added the source.
With Robert Pattinson out of the country, thousands of miles away working in Australia, Stewart has been missing him badly.
"Robert is often starting his working day when Kristen Stewart is busy, and vice versa. And he is not the best at sending texts, or keeping in touch in the first place. Kristen is angry with him because she thinks he's not giving her enough attention, it's absolutely killing her," said the source.