An Ontario court has ruled that a man who had unprotected sex after agreeing to wear a condom committed sexual assault because his behaviour invalidated his sexual partner's consent.

In a recent ruling, a judge found Anibal Rivera's actions amounted to fraud and caused a significant risk of serious bodily harm.

Ontario Superior Court Justice Nathalie Champagne said not wearing a condom against another person's wishes usurps that individual's sexual autonomy and their right to make decisions about how they engage in sexual activity.

Court heard Rivera, of Valleyfield, Que., and a woman, who cannot be identified, met on the dating website "Plenty of Fish" in October 2017 and arranged to meet at her Cornwall, Ont., home for a sexual encounter a few days later.

Prior to their meeting, court heard the woman texted Rivera to tell him condoms, which she used as birth control, were mandatory and that "no means no." Rivera agreed to those terms.

The woman told the court she reiterated her rules during their encounter but Rivera proceeded without a condom against her wishes, insisting he was "clean." Rivera testified the woman had agreed to go ahead without a condom as long as he did not ejaculate inside her.

Though the pair had planned on Rivera staying the night, court heard he left after a few minutes of small talk.

The woman told the court she went to a hospital the next day to conduct several tests, including for pregnancy and sexually transmitted infections, as well as a sexual assault kit. She contacted police a few days later.

Before his first interview with police, Rivera drafted a written statement in which he said the complainant had initiated unprotected sex, court heard. He later admitted during cross-examination that he had lied in the statement.

"This is a case of 'he said, she said' which raises issues of credibility and reliability," Champagne wrote in her ruling. "Mr. Rivera's evidence gives rise to serious issues regarding his credibility and reliability."

Rivera wrote his statement to police before investigators gave him details of the allegations against him, she said.

"His fabrication that the sexual encounter was initiated by the complainant without a condom and his assertion that she told him she could not get pregnant suggests to me he knew prior to going to the police station that the sexual encounter without a condom was the subject of the complaint," she said.

"In addition, when confronted with the fact that he drafted the statement at a time he purported to know nothing about the allegations, he changed his testimony."

The complainant's evidence that she required Rivera to use a condom and did not agree to sex without it is consistent with the conditions she laid out over text, the judge said. It is also consistent with her undergoing tests at the hospital the next day, Champagne said.

"It is improbable that she would have risked pregnancy by agreeing to sex without a condom, particularly with a stranger," the judge found.

Champagne said she drew no negative conclusions from the fact that the complainant made small talk with Rivera after their encounter or that she took a few days before contacting police.

"It would be inappropriate for me to do so and would invoke myths and stereotypes about how victims of sexual assault should act," she said.

"It stands to reason that a complainant might make small talk to keep things calm and avoid unwanted contact and it would not be unreasonable for a complainant to take some time to consider whether or not to proceed with a complaint given the stress and scrutiny of intimate details of one's life involved in the criminal court process."

Sex without a condom is a "qualitatively different" act than sex with one and the woman had only consented to the latter, the judge said.

"In my view, Mr. Rivera led the complainant to believe he would wear a condom as he had previously agreed to do so and at the last minute he penetrated her without a condom telling her it would be ok," she said.

"I find his failure to wear a condom increased the complainant's risk of pregnancy and constitutes a significant risk of bodily harm ... Her consent was therefore vitiated by this action."

While Champagne said she did not disbelieve the woman's testimony about forced oral sex and a second round of unprotected sex, the judge said the evidence had not reached the standard of proof for conviction on those allegations.