Karr, who made a confession police said was false regarding the unsolved killing of 6-year-old Jon Benet, began dating Simmons after he was cleared by police of any involvement in the child's death.
"There were times when we had lots of fun, good times but I always think most of our good times were followed by bad times immediately after," Simmons told TV's "Inside Edition. "His personality and my personality clashed, to say the least ... John is a very vocal fighter and sometimes those words hurt worse than physical pain."
Simmons revealed the police were called to their home several times but she insisted that Karr never physically harmed her.
"John would crawl up in the corner and cry before he would try to kill me or harm me," she maintained.
Regarding his claim that he was involved in the death of Jon Benet, Karr "never said that he made it up, never," Simmons said.
"Why (law enforcement) let him go so quick, I don't understand," she told "Inside Edition." "And based on things that I've seen and, I mean, many people have seen as well, it's not just me but, I think they dropped the ball too quick on that with him."