Tania Pontbriand, 40, faces two counts of sexual exploitation of a minor and one count of sexual assault while employed at a high school in Rosemere, north of Montreal.
The man, now 25, told court on Friday their first sexual encounter occurred May 19, 2002, which the accused celebrated with dog tags that read "BFF. Best Friends Forever. 19-05-02."
The trial began after Judge Francois Beaudoin denied a defence motion to have the case against Pontbriand dismissed because of delays.
The alleged victim testified he was an honour roll student in 2002 and had a normal, professional teacher-student relationship with Pontbriand, his gym and leadership teacher.
That changed during a May camping trip in 2002 when they talked all night.
He said the pair went camping alone two weeks later, when their first sexual encounter allegedly occurred and was marked with the dog tags.
He testified he was confused and didn't expect to be having an affair with a married teacher.
After a second encounter at her home, Pontbriand, who was married, told him she loved him, he testified.
At one point, the man moved out of his home after his mother forbid him from seeing Pontbriand. He said the two had to sneak around to continue their illicit affair.
He testified the affair continued but that the sex occurred less frequently as he graduated from high school and headed to college. After he left high school, they began to fight more often.
The alleged two-year relationship with the student began in 2002 when he was 15 and she was 32.
The former student did not immediately file a complaint with police and charges were only laid in September 2008.
(CJAD, The Canadian Press)