"I was getting grumpy and told Anna [his wife] she might have to go alone," Macdonald said.
He believed he worked as many as 1000 hours more than Mr Guy a year.
According to his police statement, when they finally arrived at a cafe for the dinner, Mr Guy made a comment about being late to Anna Macdonald.
That upset Macdonald and he responded by asking to know what happened.
"I was pissed off and gave him a blast about leaving work before work is done," Macdonald said.
Mr Guy stormed out of the dinner.
The next morning Macdonald "talked to Scott and said it should not have happened". They spoke about improving their communication so they could deal with problems and not "stew on" things.
Ewen and Anna Macdonald were in partnership with Scott and Kylee Guy in the family farm, with the majority shareholders being Scott and Anna's parents, Bryan and Joanne.
At an earlier meeting to discuss the future, Mr Guy had shocked everyone with his expectation he would inherit the farm.
He was also unhappy that Macdonald and his sister were moving into the family homestead and effectively getting a $500,000 home for half-price, because an interest-free $250,000 loan from Bryan and Jo Guy did not have to be repaid immediately.
While they were moving into a bigger home, he and his wife were still living in a rented property and Macdonald thought it was Mrs Guy who "had some influence over Scott's stance".
Macdonald's statement said he and Mr Guy were "competitive" but not about the farm, more with personal things like starting a family.
Earlier, evidence was given about how the police investigation swung into action after Mr Guy's death.
Detective Sergeant David Thompson said a number of theories were investigated, including a drugs link and a burglary gone wrong. Both were ruled out.
Three puppies that disappeared at the time of Mr Guy's death are alleged to have been killed by the defendant, in an attempt to create a false trail. He alerted police they were missing the day after Mr Guy was killed.
Police spent months looking at all the burglaries in the area.
There had been a suggestion Mr Guy had destroyed a crop of cannabis in maize or near the riverbed on the farm which could be why someone was seeking revenge, however Mr Thompson told the court that claim lacked any credibility. When detectives were drawing up a list of suspects they delved into Mr Guy's life looking for any evidence of drugs, criminal associations or extramarital affairs but all those inquiries "came to zero".
Instead, the list of suspects - which included known criminals and drug users, some with access to firearms - was reduced down to Macdonald.
About 18 months before Mr Guy's death, offensive graffiti was painted on his and his wife's new home, which was also damaged inside, while an old home on a trailer was burned down.
Police realised the arson and vandalism on the Guy farm would lead to the killer. An associate of Macdonald's has told police he joined him in carrying out those acts.
The Crown says Macdonald was trying to scare Mrs Guy off the farm.
"It was crucial that we needed to find the person responsible for that ... And equally the issues on the farm and other factors were leading us to look at Ewen Macdonald," Mr Thompson told the court.
Investigators found it difficult tracking down evidence on Macdonald because he was "so entwined in the family and the farm environment" that they could not make inquiries about some things without alerting him they were closing in on him.
Under cross-examination, Mr Thompson told defence lawyer Peter Coles that a rough-looking man who stank of alcohol and cigarettes who was looking for Mr Guy in the days before he was killed was never found.
Also not found was a mystery car that Mr Guy called 111 about four days before he died.
Mr Coles asked the detective about burglaries in the area and was told there had been dozens, including seven that involved the theft of firearms and ammunition, and it was not clear how much had been recovered.
