Kristen Stewart, 23, and Pattinson ended their three-year-old romance in May after the actress' affair with her 'Snow White and the Huntsman' director Rupert Sanders became public, reported Hollywood Life.
Stewart publicly apologised to Pattinson after the scandal and the couple tried to patch things up after a brief split but they finally parted ways in May.
"Kristen is convinced that what she and Rob had was one of a kind, that their love for each other was one of a kind and can never, ever be replaced," a source said.
"Kristen still misses Rob, but finds comfort in knowing that what they shared was the best thing that ever happened to her. She knows deep down inside that Rob feels the same thing, and she will be forever grateful for their relationship," the source added.