Tyler’s former roomate Dharun Ravi (AP)

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He walked briskly into the courtroom — eyes darting around nervously and clearly uncomfortable. The compact man with close-cropped hair spoke in a low baritone.

“M.B.,” the 30-year-old boyfriend of tragic Rutgers freshman Tyler Clementi, clasped his hands as he lay bare to a jury explicit details of a relationship that became fodder for dormitory bully Dharun Ravi.

“We wanted to see each other every single day,” M.B. said of his weeklong affair with the 18-year-old aspiring violinist — though he didn’t even know Clementi’s last name at the time.

“I didn’t know it until the day I picked up a newspaper and saw what had happened,” he told jurors, turning flush at times.

Clementi committed suicide days after learning that Ravi, his randomly assigned roommate, had simulcast snippets of one of their dorm-room trysts to a group of snickering fellow freshman.

M.B.’s identity is being kept secret, and the single photographer allowed in court was permitted to shoot him only below the neck.

The witness gave the prosecution its biggest victory of the trial with testimony that Ravi had a computer Web cam trained directly on Clementi’s bed.

“I noticed there was a Web cam, faced over in the direction of the bed,” he testified against Ravi, who is not charged in Clementi’s death but faces up to 10 years on bias intimidation charges.

“I just thought it was strange,” M.B. told jurors. “Being in a compromising position . . . it just caught my eye that there was a camera lens looking right at me.”

The camera was off at that moment, M.B. told jurors — but it was flicked on at least twice during that night’s encounter, according to multiple witnesses in the weeklong trial.

And Ravi was not content merely to give a few of his fellow freshmen a peep show — he tweeted about it to other pals.

Then he invited still more students from his Ultimate Frisbee team to tune in to another tryst in the dorm room a couple days later, prosecutors say. That second simulcast attempt was thwarted by Clementi finding the camera and turning it off.

During that date, M.B. could hear laughter coming from right outside Clementi’s window.

“We were both laying together in his bed. I could hear people talking in the courtyard. It sounded like people were joking,” he testified.

The testimony is highly damaging to the defense, because Ravi is trying to portray himself as merely concerned with the safety of his belongings.

His lawyers fired back at M.B. with an aggressive attack that accused him of being a creepy older man who had insinuated his way into a dorm full of college boys.

M.B.’s lawyer, Richard Pompelio, said outside court that his client is devastated by the tragedy.

“It hurts him terribly that this young man is dead,” he said. “He is a crime victim, and he has asked to be treated with fairness, and compassion, and respect and dignity.”