A witness in the Steven Boone trial broke down in tears Wednesday as he told a jury how shocked he was when someone told him the man he was sleeping with was HIV-positive.

“My heart dropped,” said the 20-year-old witness.

He said Boone’s roommate broke the news to him while he was on the 95 Baseline bus.

“He said ‘you can’t have sex with him because he’s HIV-positive and he’s got STDs up the wall,’” recalled the witness, whose voice drifted off as he became emotional. “I remember saying,’no, no.’”

The identity of the witness is protected by a publication ban.

Boone is accused of attempted murder and administering a noxious substance — HIV — to three men between January and April 2010. He is also accused of aggravated sexual assault on five men, two of whom are named as victims in the attempted murder and noxious substance charges. Boone has pleaded not guilty.

The Crown argues Boone gave the witness HIV and exposed the “realistic possibility of infection” to five other men.

The witness said he met Boone in January 2010 and engaged in unprotected sexual intercourse about nine times. Each time they had sex, the witness said he asked Boone if he had HIV.

Boone’s answer was the same every time, he said.

“It was always that he was clean,” he said.

The Crown said Boone tested positive for HIV in October 2009.

The witness told the Crown had he known Boone’s HIV status at the time they both met, he would not have engaged in unprotected sex.

The trial continues.