LOS ANGELES   –   Vittoria Ceretti, a top model, has been dating megastar Leonardo DiCaprio for more than two years. But reports say she is unhappy. Explaining the reason, the sources say Kate Winslet, a close friend of the Oscar winner, is interfering in his personal life. This is what the supermodel reportedly believes, though she “isn’t accusing Kate and Leo of hooking up. It’s not about that.”  But “what bothers her is having to share him with another woman.” As the insider explains, “Vittoria respects the friendship, but she also thinks Kate inserts herself way too much and Leo lets her.”  Moreover, it also irks Vittoria when Leonardo gets excited about Kate’s call, the source alleges. “The way he jumps when Kate calls or texts drives Vittoria crazy, but when she points it out, Leo just gets defensive, and they end up fighting.”  Not to mention, the actor reportedly places a high value on his Titanic co-star, which frustrates his girlfriend. “She says every time they hit a bump, or she tries to talk something through with him, he somehow ends up bringing up what Kate thinks or what Kate once told him about relationships.”