This undated image shows Omar Mateen, who authorities say killed dozens of people inside the Pulse nightclub in Orlando, Fla., on Sunday, June 12, 2016. The gunman opened fire inside the crowded gay nightclub before dying in a gunfight with SWAT officers, police said. (MySpace via AP)

“He just wanted to fit in and no one liked him,” he said. “He was always socially awkward.”

In Orlando, the Los Angeles Times reported that Mateen attended the Pulse nightclub possibly as many as a dozen times before the rampage. Kevin West said he had messaged Mateen back and forth over a year’s time on the gay dating app Jack’d but never met him until he saw Mateen crossing the street about 1 a.m. Sunday.

“He walked directly past me. I said, ‘Hey,’ and he turned and said, ‘Hey,’” and nodded his head, West said. “I could tell by the eyes.”

At least four regular customers of Pulse, the lesbian, gay, bisexual and transgender nightclub where the massacre took place, told the Orlando Sentinel on Monday that they believed they had seen Mateen there before.

“Sometimes he would go over in the corner and sit and drink by himself, and other times he would get so drunk he was loud and belligerent,” said Ty Smith, who also uses the name Aries.

He saw Mateen at the club at least a dozen times, he told the Sentinel. “We didn’t really talk to him a lot, but I remember him saying things about his dad at times,” Smith said. “He told us he had a wife and child.”

The Canadian Press reported Monday that Mateen had been seen there over three years.

Chris Callen recalled the eventual killer being escorted drunk from the Pulse bar on multiple occasions, including one incident where he pointed a knife at a friend. Said Callen, who performs under the name Kristina McLaughlin, “He’s been going to this bar for at least three years.”

Mateen’s father emphatically told The Post Monday that his son was not gay.

“If he was gay, why would he do something like this?” Seddique Mateen asked.

The former classmate said the group, including Mateen, went to four gay clubs in the Treasure Coast and West Palm Beach in 2006: Kashmir Night Club in West Palm Beach, Byrd Cage in Port St. Lucie, Cold Keg in Melbourne and Rebar in Port St. Lucie.

All but Cold Keg have since closed, and the owner there said he hadn’t seen Mateen.

Neither had one of the former owners of Kashmir, who said none of his former employees have reached out to him, either.

Rebar closed in February and became Tattle Tails. The owner of Tattle Tails, Johnscott Willett, said Monday that he did not recognize Mateen. Willett said he worked for nine years at Rebar and didn’t recognize him from his time there, either.

He said St. Lucie County Sheriff’s deputies visited the club on Sunday and asked if he recognized Mateen.

After hearing that Mateen had shot up the nightclub, he said he felt angry, then betrayed.

He said Mateen graduated from the academy.

Mateen never became an officer in Florida.