Aaron Hernandez may have murdered a former pal to protect his most guarded secret — that he was bisexual, a new report says.

The musclebound former New England Patriots tight end allegedly had a longtime male lover, a friend from high school, and left behind a suicide note this week addressed to a gay jailhouse lover, Newsweek said.

The suicide note was one of three found in Hernandez’s cell after he hanged himself Wednesday — the other two were to his fiancée and to his 4-year-old daughter.

Hernandez, 27, had been serving life without parole in a Massachusetts prison for the 2013 shooting murder of his former pal, semi-pro football player Odin Lloyd, a slaying that ended Hernandez’s promising career less than a year into a $40 million contract extension.

Why Hernandez threw everything away to leave his friend riddled with six bullets in the gravel of a suburban Boston industrial park has remained a mystery, even after an extensive 2015 trial.

Cops long believed that Lloyd had incriminating information on Hernandez that the player didn’t want to get out.

Law enforcement sources told the Boston Globe shortly after the player’s arrest that Hernandez feared Lloyd would rat him out in a previous double murder in 2012 — for which he was acquitted last week, just five days before the suicide.

Prosecutors only alluded at trial to the idea that Lloyd had said something to Hernandez just before his murder that destroyed his trust. A motive was never firmly established, something his lawyers noted in closing arguments.

But multiple law enforcement officials directly involved in the Lloyd murder case now believe that the ex-pal knew about Hernandez’s bisexuality and the Patriots player feared it would be made public, Newsweek said.

Lloyd “had information the football star did not want out — that he was bisexual,” the mag said.

A co-defendant in Lloyd’s murder privately confirmed to detectives that Lloyd knew Hernandez’s secret, Newsweek reported.

Co-defendant Ernest Wallace told cops that Lloyd had slurred Hernandez as a “schmoocher,” or someone who is gay, before his death, the report said.

Wallace himself referred to Hernandez as a “limp wrist” during a taped jailhouse visit with the former player’s incarcerated cousin, the report said.

Hernandez’s alleged longtime male lover was also interviewed extensively by investigators after Lloyd’s murder and was forced to testify before a grand jury, Newsweek reported.

Hernandez moved “a large amount of money” into the lover’s bank account shortly before his arrest, Newsweek reported.

The ex-player’s prison boyfriend “is now on 24/7 suicide watch,” Newsweek said.

Hernandez was so intent on killing himself that he jammed cardboard into the frame of his cell door to thwart guards rushing to aid him — and poured liquid soap on the floor of his cell so he’d have no traction to struggle free of his bedsheet noose if he lost his nerve.

Lawyers for the Hernandez estate said they are mulling a negligence suit against Massachusetts corrections officials.