Robert Pattinson is supposedly so jealous of the sex scenes girlfriend Kristen Stewart will have with Viggo Mortensen in their upcoming movie, On the Road, that he says he is going to be on set when she shoots them. YOU CAN’T SAY ROBERT PATTINSON DOESN’T TAKE AN INTEREST IN KRISTEN STEWART’S CAREER…IN FACT, HE’S TAGGING ALONG ON THE SET OF HIS GIRLFRIEND’S NEXT MOVIE… R-PATZ REALLY WANTS TO BE THERE FOR K-STEW WHEN SHE FILMS SOME SCENES FOR HER UPCOMING FLICK,"ON THE ROAD". SOUNDS SWEET, RIGHT? UH NOT SO MUCH. WE HEAR TOTALLY JEALOUS OF THE RACY SEX SCENES SHE’LL SHARE WITH HER HOT OLDER CO-STAR VIGGO MORTENSEN. A SOURCE TELLS HOLLYWOOD LIFE.COM, "There are a lot of sex scenes including a threesome, and Rob wants to make sure that it’s all pretend from the start and finish of the film." ROB REPORTEDLY WANTED KRISTEN TO PASS ON THE SEXY ROLE ALTOGETHER, BUT SINCE SHE DIDN’T, THE SOURCE SAYS, "he’s going to be there, even if it makes her uncomfortable to have him around."