Brad Delp was her “best friend,” someone she could turn to after a bad date, a breakup, or just a tough day. And for nearly 2½ years, Meg Sullivan also lived with the famed singer for the band Boston, staying in a spare bedroom at his house on Academy Avenue in Atkinson, N.H. By all accounts, the arrangement was platonic; Pamela Sullivan, Meg’s older sister, was Delp’s fiancee.

But the relationship between Delp and the Sullivan sisters took a dark turn on the morning of Feb. 28, 2007. That’s when Meg Sullivan discovered a hidden camera that Delp had placed in her bedroom. She confronted Delp and fled to her boyfriend’s place, marking the start of a personal crisis that appears to have dominated the last nine days of Delp’s life. On March 9, Pamela Sullivan found Delp, 55, dead in his bathroom. The deeply depressed singer had killed himself by lighting two charcoal grills and letting the carbon monoxide overtake him.

These previously unreported revelations regarding Delp’s relationship with Meg Sullivan have become a central piece of the now two-year-old defamation lawsuit filed by Boston founder Tom Scholz against the Boston Herald.

Following Delp’s death, Herald stories, quoting an interview with Delp’s former wife, Micki Delp, and material from unnamed sources, seemed to suggest that Scholz was to blame for Delp’s suicide. A week after his 2007 suicide, the Herald’s Inside Track writers Gayle Fee and Laura Raposa quoted Micki Delp in a piece with the headline, “Pal’s snub made Delp do it: Boston rocker’s ex-wife speaks.’’ They wrote about the conflicts between Scholz and past band members and stated that Micki Delp said her former husband was “upset over the lingering bad feelings from the ugly breakup of the band Boston over 20 years ago’’ and “driven to despair’’ by recent changes in the group. It was, the Herald reported, “the last straw in a dysfunctional professional life that ultimately led to the frontman’s suicide, Delp’s ex-wife said.’’

For the lawsuit, Herald attorneys point to voluminous testimony from former Boston members, other local musicians, Delp’s doctor, and Delp’s friends, including Meg Sullivan, many of whom say the singer didn’t like Scholz, desperately wanted to quit the band, and felt tormented by his role as middle man in an ugly conflict between Boston’s founder and former band members. All of this was summarized in a 140-page statement filed by the Herald in April.

Scholz’s attorneys argue that the guitarist didn’t cause Delp’s depression and that the singer’s personal problems — deepened by his fiancee’s affair in the summer of 2006 and the discovery of the hidden camera in her younger sister’s bedroom — led to his suicide.

Meg Sullivan, who now lives in California, did not respond to requests for an interview, but her taped depositions in the lawsuit, along with e-mails to and from Delp filed as evidence, shed new light on the tragic story of Delp and the complicated history of Boston, a band that soared to fame in the 1970s before becoming consumed by decades of conflict.

Scholz, a gawky MIT graduate, created much of the music on the band’s 1976 debut in his basement, layering guitars, keyboards, and Delp’s soaring vocals into an album that is still the second biggest-selling in US rock history. With hits such as “More Than a Feeling” and “Don’t Look Back,” the band — made up of Scholz, Delp, and three other musicians — went on to play sold-out arenas around the world.

But personality and business conflicts led to a series of lawsuits between Scholz and former members. Over the years, only Delp remained in Boston, which has continued to tour even after his death by hiring other singers.

In Delp’s last days, the crisis involving Meg Sullivan weighed heavily on him, according to legal filings examined by the Globe.

On Feb. 28, Meg Sullivan discovered the battery-powered camera in her bedroom when it fell into view. The next day, Delp wrote her an emotional e-mail saying, “I feel sick about this, and deservedly so.” She didn’t respond.

On March 2, Delp had a show with his Beatles tribute band, Beatlejuice, at the Sit ’n Bull pub in Maynard. Todd Winmill, Meg Sullivan’s boyfriend, was scheduled to work as a sound engineer for the show; Winmill had also been a sound man for Boston. Delp huddled in Winmill’s car before the gig, according to Winmill’s testimony.

“He essentially apologized for about a half-hour,” said Winmill. “And then I told him he had to tell Pamela. He didn’t like the thought of having to do that.”

At 2 a.m. on March 3, Delp e-mailed Meg Sullivan again, pleading for forgiveness.

“I want to try and make you understand that I consider myself a decent person who made a dreadful error in judgment,” wrote Delp. “I acted out of some impulse that is still not completely fathomable to me.”

He called his action an “aberration” and compared it to Pamela Sullivan’s affair the previous summer — an affair that emerged in previous testimony and was confirmed last year by Pamela Sullivan in a Globe interview. At one point, Delp had tried to set up tracking devices on her computer to catch her in an affair, but in the end, she admitted the infidelity and the two eventually made plans to get married.

Pamela Sullivan did not respond to recent requests for an interview. Attorney Jeffrey Robbins, who is representing the Herald, declined to comment on the case. Scholz attorney Nicholas Carter also declined comment.

The e-mail Delp sent in the early morning hours of March 3 led to responses from Meg Sullivan and Winmill.

Winmill pushed Delp to tell Pamela Sullivan about the camera. He gave him one day to do it because, he wrote via e-mail, it was unfair to ask Meg to keep the secret from her sister.

It is because of [Meg’s] regard for you that she has given you this opportunity to tell Pam yourself,” wrote Winmill, who now lives in California and did not respond to recent interview requests. “It is probably the best way for her to hear it, but please understand, and this is not a threat, but understand that she will find out.”

Delp asked if he could have until March 5, when he planned to tell his fiancee on the phone.

That day, Delp started purchasing tubes and vents at the Home Depot in Plaistow, N.H., according to receipts filed in court. Delp’s idea was to hook these up to the exhaust pipe of his yellow Volkswagen Bug. This, he would later write in a note taped to his garage, was for a backup suicide plan.

On the night of March 7, according to Winmill’s deposition, he and Meg Sullivan showed up at Delp’s home to pick up more of her things. It was an unpleasant experience, as described in Meg Sullivan’s deposition. Winmill yelled and swore at Delp, who repeatedly apologized and was in tears, according to Sullivan.

The next day, Delp bought a pair of charcoal grills at Walmart. And that night, instead of returning to Delp’s house, Pamela Sullivan stayed at an apartment they had rented for her. She found Delp’s body the following day.

The Herald, in a pair of recent articles, has focused on Delp’s relationship with Scholz, describing what it says were the singer’s negative feelings about Scholz as relayed by the testimony of numerous witnesses. The newspaper has referenced the events of Feb. 28, when Meg Sullivan discovered the camera, only as “an extremely upsetting and embarrassing incident” that Scholz has raised in the case. The Herald has not mentioned Meg Sullivan or the camera.

The Herald also wrote that before the camera incident, Delp purchased items the paper says were apparently used in connection with his suicide, but the evidence here is unclear. The Herald noted that according to court records, Delp bought 9-volt batteries and duct tape on Feb. 27. A carbon monoxide detector was found on Delp’s bed with the 9-volt battery removed, according to the police report. The hidden camera also used a 9-volt battery, court records show. Delp bought gray, metallic duct tape at Home Depot, according to the Herald’s court statement, but the police report stated and showed in pictures that brown duct tape was used to seal the bathroom door.

In a statement, Herald spokeswoman Gwen Gage said the Herald’s coverage of the matter has been “both accurate and excellent” and assailed the Globe’s coverage as “journalistic rivalry getting the better of editorial judgment.”

Other evidence has also emerged. In her testimony, Meg Sullivan discussed her role as a confidant for Delp when he discovered his fiancee’s affair. She also detailed what she said were Delp’s complaints about Scholz and the psychological toll his relationship with Scholz placed on him.

“I believe that Tom Scholz and Boston caused the depression which caused Brad to put a camera in my bedroom,” Meg Sullivan said at one point.

Delp did not mention Scholz or Boston in his e-mails to Meg Sullivan and Winmill after the camera was found. But he did reference Pamela Sullivan’s affair.

“I do love your sister, as incongruous as that may seem at the moment,” he wrote. “Maybe the emotional roller coaster that I was on this past summer has in some way something to do with what possessed me to do such an irrational and out of character thing.”

Before sealing himself in his bathroom, Delp left separate suicide notes in envelopes for his former wife, his two adult children, and Pamela Sullivan. He left a fourth note labeled “Meg and Todd.”

In his note to the couple, Delp apologized for causing them pain and told them they were not to blame for his death.

“I have had bouts of depression and thoughts of suicide since I was a teenager,” Delp wrote.

He went on to talk of Pamela Sullivan, whom he had planned to marry later that year.

“She was my ‘ray of sunshine,’ but sometimes even a ray of sunshine is no substitute for a good psychiatrist.’”

Bradley Edward Delp