Complex sentence: Her best friend, Bárbara Fuenmayor, angry that she has always been forced to live in Sofía's shadow, is not happy with her return, especially after discovering that before leaving Acapulco, Sofía had slept with her boyfriend, Nico.
Split into simpler sentences: Her best friend, Bárbara Fuenmayor, angry that she has always been forced to live in Sofía's shadow, is not happy with her return. Bárbara is especially unhappy after discovering that before leaving Acapulco, Sofía had slept with her boyfriend, Nico.