Complex sentence: The relationship was controversial among Dallas Cowboys fans, and she was blamed for Romo's poor performances giving her the nickname "Yoko Romo" in reference to Yoko Ono, who many Beatles fans blamed for "ruining" John Lennon.
Split into simpler sentences: The relationship was controversial among some Dallas Cowboys fans, and she was blamed for Romo's poor performances. Some of the Cowboys' fans gave her the nickname "Yoko Romo" in reference to Yoko Ono, who many Beatles fans blamed for "ruining" John Lennon.