LOS ANGELES — Robert Pattinson will only take Kristen Stewart back if she marries him because the 26-year-old actor wants his “Twilight” co-star to “truly commit” to him. Pattionson — who was left devastated when his ‘Twilight' co-star publically admitted this summer that she had cheated on him with her “Snow White and the Huntsman” director Rupert Sanders — is said to be “desperate” to get back with the brunette beauty, but he wants her to “truly commit” to him. A source said: “Rob told Kristen the only way he can forgive her affair is if she truly commits to him. “Rob has been keen to marry Kristen for quite a while and he doesn't want to get back with her unless he knows she means it for life too. “Although Kristen broke Rob's heart he has realized he can't live without her. He never stopped loving her and he believes she still loves him. He is desperate to make it work and wants to give her another chance but not unless she proves she really wants it too.” — Agencies