John and Katy had a very dramatic relationship, and each of them had jealousy issues, according to Radar Online.
"John and Katy together were like a volcano just about to go off," a source says. “Their relationship was incredibly volatile, stemming from the jealousy they both harbored deep inside."
John apparently was quite the flirt, whereas Katy would frequently compare John to another bad boy in her life: her ex-husband, Russell Brand.
“Sure, Katy was unhappy that John constantly flirted with other girls and played up his heartbreaker image, even when she was standing next to him," the source continues.
"But, Katy gave it back," the insider adds. "She knew that she could push John’s buttons by comparing his flaws to what she saw was great in Russell, which he hated!"
In fact, John wasn't thrilled about the fact that Katy and Russell have stayed friends since their split.
“Katy and Russell still talk to one another, and that was another thing that irked John," the source says. "He’s never been in a relationship where he wasn’t the main focus all the time, and it bothered him."
John recently addressed the relationship while talking to Ellen DeGeneres this week, saying, "Coupling is a tricky thing."
In other words, we probably shouldn't be waiting on
the world John and Katy's relationship status to change.
Source: Radar Online