Christopher Lumsden, 52, used a kitchen knife to stab his wife, Alison, in the neck, face and back as she sat at a dressing table in their home in Altrincham, Greater Manchester.
Five days earlier Mrs Lumsden, 53, had told her husband she was having an affair with a family friend.
Mr Lumsden, a partner at Pinsent Biddle in Manchester, admits killing his wife and blames an "abnormality of mind" but denies murder. A jury at Manchester Crown Court must decide whether he is guilty of murder or manslaughter.
The court heard that Mr Lumsden and his wife, who have two children aged 20 and 17, met in London in the late 1970s when he was working as a trainee solicitor and she was working for the auctioneer Sotheby's.
They moved to Altrincham in 1985 and lived in a large house. The court heard that Mr Lumsden was a respected lawyer working long hours. His wife was "vivacious" and sociable.
"On the face of it, their marriage was successful and happy, and had been for many years," said Charles Chruszcz QC, for the prosecution.
The jurors heard things began to change in November 2004 when Mr Lumsden was diagnosed with a muscle-wasting disease.
Mr Chruszcz said: "There is evidence that from about the time the diagnosis was made, the Lumsdens' relationship changed and was apparently less than happy."
In February last year the court heard that Mrs Lumsden began a relationship with a "family and social friend", Roger Flint.
The court heard that on 11 March last year Mrs Lumsden told her husband about the affair and said that she wanted a divorce.
The court heard that Mr Lumsden began considering his financial and social position. Notes found in his office referred to excluding his wife from his will and reducing her share in assets.
On 16 March, Mrs Lumsden and Mr Flint had dinner at a restaurant in Plumley, Cheshire, and drove back to Altrincham. At 10.40pm that night Mr Lumsden phoned his sister to confess to killing his wife. "His sister thought he was virtually incoherent at the time," Mr Chruszcz said.
His sister Elizabeth and her husband drove to the house where they found Mr Lumsden in blood-soaked pyjamas and his wife lying dead on the bedroom floor.
The jurors were told that Alison Lumsden suffered "horrific injuries". Most of the injuries were stab wounds on the neck area, but she also had wounds on her face and back. The deepest injury was 13cm (5 inches). The trial continues.Reuse content