After the twin towers fell, they grieved together: the firefighter’s parents, his fiancée and his best friend.

On Thursday, seven years later, the mourners were together again, but separated — by courtroom furniture, and by one of the more bitter legal disputes the World Trade Center attack has produced.

Firefighter Kevin Prior’s fiancée, Doreen Noone, is seeking to collect $37,600 a year in his pension benefits. Firefighter Prior’s parents, Gerard and Marian Prior, say that she is not entitled to the money and that it should go to them.

Firefighter Prior’s childhood best friend, Sgt. Edward Wheeler of the New York Police Department, who was to have been the best man at the firefighter’s wedding, ended up marrying Ms. Noone three years after 9/11. On Thursday, he testified that the rift with the Priors had compounded his grief.

“Me and Doreen were the two closest people in the world to Kevin besides his family,” Sergeant Wheeler, who works in a Brooklyn precinct, said in State Supreme Court in Brooklyn. “Now we don’t talk. It’s the most surreal thing I’ve ever experienced.”

The determination of who will get the pension turns on the definition of “domestic partner” in a state law passed in 2003 to allow companions, and not just spouses, of police officers and firefighters killed on 9/11 to collect their pensions.

The law defines a domestic partner as someone who showed either “unilateral dependence or mutual interdependence” with the deceased based on a “nexus of factors.” They include, besides intent to marry, “common householding, shared budgeting and the length of the personal relationship.”

The two sides offer starkly contradictory accounts of Ms. Noone’s relationship with Firefighter Prior. Ms. Noone and Sergeant Wheeler say that she and Firefighter Prior lived together in his parents’ basement for a year until the day he died. Firefighter Prior’s parents say no such thing ever happened.

Someone is not telling the truth.

While the Priors concede that Ms. Noone and Firefighter Prior were engaged — they had reserved a church and a reception hall, and Firefighter Prior had bought Ms. Noone an $8,000 ring — they say that she fails to meet any of the other criteria.

“She did not live with him,” Marian Prior, a retired bookkeeper, said on Tuesday at the office of her lawyer, Norman H. Siegel. “He did not support her financially. They didn’t share budgeting. All that happened was they had plans for a wedding, and those plans were interrupted.”

A fair amount of money is at stake. If the Priors win, life expectancy tables predict they would gain more than $800,000 in monthly payments over the rest of their lives. If Ms. Noone, 36, prevails, actuarial tables predict she will get about $2.6 million over the course of her life. The Priors, who have already collected an estimated $1.5 million in survivors’ benefits, say their suit is not about money but about correcting the record of their son’s life.

“When we buried Kevin,” said Mrs. Prior, 62, “we buried all hopes for the future. All we have left is memories, and that memory has to be the truth.” Kevin Prior, 27, was a member of Squad 252 in Bushwick.

Ms. Noone, a teacher in Nassau County who began dating Kevin Prior in 1997, has sworn in court papers that he lived with her and her roommate for eight months in the late 1990s. She said he paid most of her bills for a while when she was studying to be a teacher.

And she said that for the last year of his life she stayed with him in his room in the basement of his parents’ house in Bellmore, on Long Island, when he was not on duty at his firehouse in Brooklyn, returning to her own parents’ house on those nights.

“We shared the same bed four to five nights a week,” she said on Wednesday. “His parents were well aware that I was down there,” though they did not approve, she said.

After Firefighter Prior’s death, Ms. Noone said, she stayed with the Priors for several weeks.

False, false, false and false, the Priors said.

“She was never allowed to be an overnight guest, nor was any of our boys allowed to have girls overnight,” said Gerard Prior, 66, a retired police officer. The Priors said that their son did not support Ms. Noone, though they acknowledge that over the course of three years he paid more than $7,000 of her bills.

After Firefighter Prior died, his best friend and his fiancée found consolation in each other. In a year or so they started dating. In July 2004, a year after Ms. Noone applied for the pension benefits and four days before she was to be married to Sergeant Wheeler, she was sued by the Priors.

The case is being heard by a judge, Laura L. Jacobson, without a jury. In their suit, the Priors seek to overturn the decision of the Fire Department’s pension board to award the pension to Ms. Noone.

In his testimony on Thursday, Sergeant Wheeler, 35, supported Ms. Noone’s version of events. Kevin Prior did move into Ms. Noone’s apartment in 1997 and lived there with her and her roommate for months, he said. “I used to call him Jack from ‘Three’s Company,’ ” he said.

When Firefighter Prior moved back to his parents’ basement, Sergeant Wheeler said, his bedroom was filled with Ms. Noone’s shoes and toiletries. “Hair spray, baby powder, perfume, gel,” Sergeant Wheeler said. “I never saw a woman use so many products.”

After 9/11, he said, when he would go to the Priors’ house at 4 a.m. to update them after a 12-hour shift at ground zero, Ms. Noone would be asleep in a back bedroom.