Stewart and Sturridge are starring together in the new movie On The Road. The pair allegedly used to fight for Pattinson's attention but have now built up a friendship of their own.
An insider told In Touch Weekly: "Kristen was always jealous of all the time Tom and Rob spent together.
"But Rob intervened and helped make peace between the two - a move he may now regret."
The source added: "Kristen's telling friends that she's falling for Tom, as he has all of Rob's great qualities without the baggage - Rob's fear of commitment and the intense scrutiny their relationship brings."