"Their relationship has been tumultuous since day one," a mutual friend of the couple toldUs Weekly. "They're either extremely happy or they can't stand each other."
The Bachelorette couple, who currently live in San Diego, reportedly become different people when they are together and frequently get into big fights because they're stressed over their busy work schedules.
"They bring out the worst in each other," another source told Us.
According to another friend of the pair, Fedotowsky got extremely upset after one brawl in particular and she and Martinez are simply unhappy together.
"Ali was in tears," the source said. "She's miserable in the relationship and he is too."
The couple had set a date for their wedding earlier this year but postponed it when Fedotowsky broke her femur in early June in a kickboxing session and underwent surgery later that month.
"The decision to postpone [the wedding] was very difficult. I definitely shed some tears. But I want to walk down the aisle. I don't want to limp down the aisle," Fedotowsky told People in August.
While the couple -- who got engaged during The Bachelorette's sixth-season finale broadcast which aired in August 2010 after Fedotowsky selected Martinez as her final suitor -- had to hold off on getting married, the Bachelorette insisted the wedding cancellation didn't stem from doubts or cold feet.