Complex sentence: In 2009, Rossellini developed a romantic relationship with Italian Grand Prix motorcycle road racer Valentino Rossi, whom she met at the MotoGP Catalan Grand Prix in Montmeló, The pair ended their four-year relationship in the summer of 2013.
Split into simpler sentences: In 2009, Rossellini developed a romantic relationship with Italian Grand Prix motorcycle road racer Valentino Rossi, whom she met at the MotoGP Catalan Grand Prix in Montmeló. The couple ended their four-year relationship in the summer of 2013.