The cases have put attention back on the 1970s version of Boston, while also thrusting a group of lesser-known figures into the band’s saga, including Delp’s fiancee Pamela Sullivan and Richard Kilbashian, a sometime soundman for Delp’s Beatles tribute band, Beatlejuice. Their stories, along with those presented by others in testimony, provide a portrait of a deeply depressed man who, because of his own aversion to conflict, kept his true feelings from many who considered themselves closest to him.

The band’s history is particularly tangled because of marriages by members, with the dueling alliances they created, and because Scholz and Delp remained the only clear constants in an ever-changing group lineup. Even after Delp’s death, Boston continues on with Scholz, other musicians, and new singers.

Scholz’s legal team is contending that Delp’s problems with his fiancee led to his demise, while his opponents point to the decades of dissension within the Boston family tree — a fracturing that deeply troubled Delp. A Globe examination of hundreds of pages of depositions, affidavits, e-mails, and other court filings linked to the lawsuits — one against Delp’s ex-wife, Micki, the other against the Boston Herald — provides a fascinating backstage view of a band that has sold more than 30 million albums over the years.

Now a pair of defamation lawsuits, filed by Scholz in the wake of Delp’s suicide, have exposed new details about the bitter turmoil within the band that preceded Delp’s death. And they have led to revelations about the never-before-reported relationship problems that burdened Delp in the last year of his life.

The sensation of their rise was matched by the bitterness of the breakup of the original five members, who last performed together in 1979. Scholz and the three other musicians, later cast from the band, have battled in the press, courts, and Internet ever since. And no part of the feud has been as ugly as the latest: the fight over who or what caused Brad Delp, the man in the middle, to take his life in 2007.

They became Boston, a band that dominated the FM airwaves through the 1970s with hits such as “More Than A Feeling’’ and “Don’t Look Back.’’ Boston’s 1976 debut remains, at 17 million copies, the second biggest-selling in US rock history. It launched Scholz, Delp, and the band’s three other members into a world of sold-out arenas from California to Copenhagen.

In his basement, the gawky engineer fresh out of MIT painstakingly recorded layers of guitars, keyboards, and bass until he got it right. But it wasn’t until Tom Scholz, the stubborn perfectionist, met Brad Delp, the dark, complicated singer with the soaring voice, that those basement demos came alive.

On March 16, a week later, the Herald’s Inside Track writers quoted Micki Delp under the headline, “Pal’s snub made Delp do it: Boston rocker’s ex-wife speaks.’’ In the story, the Herald’s Fee and Raposa stated that Micki Delp, who was married to the Boston singer from 1980 to 1996, said her ex-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 band, specifically that co-vocalist Fran Cosmo had been “disinvited’’ from an upcoming tour. 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.’’

“I take complete and sole responsibility for my present situation,’’ Delp wrote. “I have lost my desire to live.’’

Another note, left on a bedroom door, warned of the carbon monoxide and alerted whomever discovered him to check on Floppy, their cat.

Delp hauled two hibachi grills into the bathroom, along with a photograph of Sullivan and a bottle of Sam Adams. He sealed the door with duct tape, lit the charcoal and rested his head on a pillow. That’s where he died. Sullivan found him on March 9.

‘Lost my desire to live’ Brad Delp was alone that Thursday night. His fiancee, after going out for drinks with friends, stayed over in the Exeter, N.H., apartment they had rented for her a few months earlier, when things were not going well. Sometime before or during the night of March 8 and afternoon of March 9, 2007, Delp wrote four notes — for his children, his ex-wife, Sullivan, and Sullivan’s sister — and sealed them in separate envelopes.

For three years, Kilbashian kept what he knew to himself. He watched in dismay as a series of Boston Herald stories, based on an interview with Delp’s ex-wife, Micki, and material from unnamed sources, seemed to point the blame toward Scholz. It wasn’t until 2010, when Scholz filed a defamation suit against the Herald and its Inside Track columnists Gayle Fee and Laura Raposa, that Kilbashian hesitantly stepped forward.

As the fall of 2006 turned to winter, Delp fixated on whether he could trust Sullivan. She was moving out of the house in Atkinson, N.H., he e-mailed Kilbashian, but then a few weeks later, they were making plans to get married. Delp’s mood shifted, sometimes daily. Then he was gone.

The singer had never opened up much to his bandmates. But he trusted Kilbashian and reached out to him for help. Delp told Kilbashian that he had discovered his girlfriend, Sullivan, was having an affair after she mistakenly left a Gmail message open on their computer. Could Kilbashian, who had some technical savvy, help him track Sullivan’s correspondence?

In the year leading to his death, Delp and Kilbashian had grown closer. The night of that phone call, Kilbashian was planning to go see Delp play a gig with Beatlejuice.

It was March 9, 2007. This was no accident, Kilbashian knew, growing hysterical. Brad Delp, 55, had killed himself.

The principals in this suit — including Micki Delp, Scholz, the Boston Herald, Connie Goudreau, and Kilbashian — declined comment. But reams of testimony and filings examined by the Globe provide their voices.

Meanwhile, Scholz’s attorneys argue that he had nothing to do with Delp’s depression and blame his state of mind on his up-and-down relationship with Sullivan.

Micki Delp’s attorneys contend that her comments to the Herald are “non-actionable’’ opinion and that, because they are based on what she says her ex-husband told her over time, Scholz can’t prove that she doubted the truth of her statements. The Herald’s attorneys say that Micki Delp was accurately quoted. They have been building a case around testimony and documents from Micki Delp, friends of Brad Delp, and ex-Boston members Sheehan and Goudreau, who say the singer disliked Scholz and desperately wanted to quit the band but feared that Scholz would make his life miserable if he did.

Relationships questioned Ultimately, a jury may be asked to decide what caused Delp to kill himself. That issue forms the crux of the cases.

After the Herald items ran, “I felt like a disgrace and a hoax,’’ Scholz stated in a court filing. “I did not want to leave my house. I suddenly noticed people staring at me in an odd way and avoiding me altogether.’’

In his testimony for the lawsuits against Micki Delp and the Herald, Scholz said the humiliation brought on by the Herald’s March 16 article made it hard for him to work on music, eat, or sleep. The accusations strained his new marriage. He stopped ice skating — the “one physical activity I routinely enjoyed’’ — and had to cancel vacations and fund-raisers because he wasn’t well enough to fly his single-engine plane.

In suing the newspaper, Scholz’s attorneys contend that Fee and Raposa published false and fabricated statements attributed to Micki Delp and unidentified sources, and that the Track writers disregarded warnings that Micki Delp had a personal vendetta against Scholz.

Late in 2007, Scholz filed defamation lawsuits against Micki Delp and Connie Goudreau. He sued the Herald in 2010. Connie Goudreau has since settled her case, stating that Scholz had nothing to do with Delp’s suicide. But the Micki Delp and Herald cases are unresolved, and they have been consolidated in Suffolk Superior Court.

Delp was tangled in complicated loyalties: While he had stayed in the band with Scholz, he remained close and played music with Goudreau, bassist Fran Sheehan, and drummer Sib Hashian, all of whom had complained bitterly about Scholz, Boston’s mastermind, after leaving the band.

Similar statements followed in subsequent Herald stories. In addition, Micki Delp’s sister Connie Goudreau attacked Scholz on the Internet and e-mailed the Inside Track as a source, according to court filings. Goudreau is the wife of guitarist Barry Goudreau, one of the three former members from the band’s 1970s heyday.

From the testimony, it appears Delp confided in fewer than a handful of friends about his problems with Sullivan. That tiny circle included Rick “Skillet’’ Kilbashian, who Delp first met in 1986 when Kilbashian was working as a tour manager.

Kilbashian has testified that Delp’s suicide had “nothing to do’’ with Tom Scholz and that his problems with Sullivan consumed him. E-mails between Delp and Kilbashian underscore the singer’s struggle.

“On the surface things are going OK but I’m getting a very strange vibe lately,’’ Delp wrote on Nov. 27, 2006, in a note with a subject line “I’m weakening.’’ “Unfortunately I think her Gmail account has the answers I need.’’

Delp wrote Kilbashian, in another note, that they were “at least publicly, committed to try and work things out.’’ But in the fall of 2006, he helped Sullivan move out to the Exeter apartment. Some days, Delp wrote, he felt hopeful. Other days, he fixated on how to install software that could covertly track her keystrokes — and thus her e-mails and online chats.

Some friends said that Delp and Sullivan had patched up their problems and he was thrilled to be getting married; some e-mails between the two support this happier view. The friends also dismiss Kilbashian, saying he had little contact with Delp after the engagement. But Delp’s ex-fiancee Patricia Komor, in an affidavit, described a man who viewed his wedding with resignation, not joy. She said that when Delp proposed to Sullivan on Christmas Day 2006, he had called her to explain.

“Brad told me that Pamela had raised the idea of marriage with him,’’ she stated. “Brad told me he was too old to be alone and that he was not going to find anyone else.’’

Emotions remain raw Pamela Sullivan does not like to follow the controversy closely. But she knows that she’s been sucked into it. On a recent evening, she agreed to an interview at the Hardcover restaurant in Danvers, near her work.

Sullivan, 39, still wears her engagement ring. She speaks slowly and with pauses, sometimes needing a minute to compose herself, often removing her glasses to dab an errant tear.

The legal fight, she said, does not make life easier.

“I wish the entire thing would go away,’’ Sullivan said. “Everyone involved wishes it would go away.’’