Describing his relationship with his wife Isabelle Gaston, Guy Turcotte broke down in tears while taking the stand at his trial for the murder of his two children.

He said of his relationship that he was sad, hurt and disappointed by Gaston’s affair with a family friend, especially after he began to feel Gaston’s lover was taking over his role as father and playing with the kids.

Turcotte has admitted to killing son Olivier and daughter Anne Sophie but has pled not-guilty to first-degree murder charges, contending he was criminally insane.

On the day of the murder, Turcotte said he felt shattered when he discovered Gaston had changed the locks on the house. That night, after the kids were in bed, he went on the Internet and read emails between Gaston and her lover and said he realized then how much he was hurt and wanted to die.

He remembered drinking glasses of methanol and picturing himself dead on the bed and thinking he didn’t want his children to find himself like that, so he decided to take them with him. He also described standing in their rooms with a knife.

In cross-examination, the prosecutor asked Turcotte if he had selective memory, because he could recount certain events but not others.

Turcotte replied that he did not.

The cross-examination continues on Wednesday.