Matthew Pyke and his girlfriend, Joanna Witton, of Nottingham, U.K., met David Heiss, from Limburg, Germany, on their Advance Wars online gaming forum.
Heiss now stands accused of murdering Pyke, a computer science student at Nottingham Trent University, after making several surprise trips from Germany to visit Pyke and his girlfriend and allegedly becoming obsessed with Witton.
Jurors were presented on Tuesday with images of Pyke's computer, on the side of which he was said to have written the first three letters of Heiss' name in his own blood as he lay dying from 86 stab wounds to his body.
Witton had earlier given evidence from behind a curtain and said that her and Pyke's social life had largely revolved around their love of gaming.
She said that Heiss had become increasingly obsessed with her over a six-month period, despite never having seen her in person. He made two surprise visits to their Nottingham home and refused to stay in a hotel.
"I started blanking him as if to say leave me alone. I was afraid he was going to turn up again and I didn't know what he was capable of," she told the court.
She added: "I was willing to smash my laptop up if it meant that I would never speak to him (Heiss) again. I was ready to run away."
The jury also heard that during a conversation with another gamer, Heiss had said he wanted to smash Pyke's head against a wall.
On September 19, 2008, the day after celebrating the couple's third anniversary, Witton went to work, and, after failing to make contact with Pyke, returned home to find him dead.
The 21-year-old Heiss gave evidence in his defense Tuesday. He said he hadn't meant to kill Pyke. He had simply flown to England to confront him and Witton after they had used the online forum to allegedly make disparaging remarks about him. The couple had blocked him from their site and from IM.
"I thought that once he (Pyke) stepped outside I would give him a beating. It wasn't my intention to put him in hospital, it wasn't my intention to break any bones," Heiss told the court.
He continued: "At some point we started to punch each other. He was on his back and I was sitting on him. The next thing I felt was something inside my knee. I didn't really feel any pain and I looked down and saw it was the knife. I was terrified."
The knife allegedly belonged to Heiss and had been in his belt.
"I was trying not to let him attack me. I grabbed his arm and shook it and smashed it against the wall. I was so afraid that he would stab me again but then I stabbed at him," testified Heiss.
The court also heard that police had allegedly found a suicide note, written in such a way as to appear they were the words of Pyke, in Heiss's suitcase. Police gave evidence that, in an interview with them, he said he had written the note to "cheer himself up".
Heiss denies murdering Pyke.