The ROBERT PATTINSON and KRISTEN STEWART rumour-mill is about to go into overdrive - amid reports she's dumped her longterm boyfriend.Kristen has apparently broken things off with her beau of three years, actor MICHAEL ANGARANO, after falling head-over-heels for her Twilight co-star, Rob.According to reports Kristen has been in Los Angeles for the past ten days - after returning from shooting New Moon scenes in Italy.During the shoot a photographer captured Rob and Kristen in a passionate embrace during filming of a scene - and the obvious chemistry has set tongues waggingBut since Kristen's return to LA, where Michael is based, the ‘couple' have not spent any time together at all - in fact, according to reports "they weren't spotted together at all".While Kristen, 19, and Michael, 21, were both in the city between May 31 and June 6, she reportedly spent her time on an Allure magazine photo shoot and made rounds to production studios to discuss film projects. Meanwhile, Michael was reported to be holed up at his parent's Woodland Hills, home, playing basketball. "They never crossed paths," sources say.The reports come after Rob, who is keen to get serious and go public - apparently gave Kristen an ultimatum - to choose between him and Michael. According to magazine reports, sources say: "Robert is completely frustrated. If Kristen isn't interested in a serious relationship, she needs to tell him so he can move on," Insiders say Rob has now given Kristen a couple months to sort things out while he's in New York City, filming his new indie flick Remember Me."He's asked her to choose between him and Michael this summer," says the source. "Robert's not willing to be strung along."And now even Twilight director Catherine Hardwicke has hinted that the pair are dating in real-life. She says: "People love to talk, so let them have fun talking. "I think they have an interesting, wonderful connection, so you know...What does dating mean? I don't know. I couldn't say." Could this be the start of RobSten?