John Shaughnessy, 30, a hospital manager, of Vardens Road, Battersea, south-west London, told the court he began sleeping with Michelle Taylor a year after his engagement. 'I just looked on Michelle as a friend who was always offering to help to do things but I did not have any stronger feelings than that. Alison, I loved,' he said.
Michelle Taylor, 21, and her sister Lisa, 18, of Kemble Road, Forest Hill, south-east London, both deny murdering Mrs Shaughnessy, 21, on 3 June 1991. She had been stabbed 54 times.
Mr Shaughnessy said he met his wife in 1986 and they married in June 1990. He met Miss Taylor in 1989 at the Churchill Clinic, in Lambeth, south London, where they both worked. 'She was working in the accounts department. Our departments liaised with each other and I found myself developing an attraction for her,' he said.
Although he slept with Miss Taylor 'about twice a month', Mr Shaughnessy said that he tried to end the relationship. 'I said I wanted to be good friends, nothing more elaborate. I made it clear I did not want our sexual relationship to continue. She agreed at first . . . But she always came back again, being a bit forward and things like that.'
Mr Shaughnessy said he did not tell his wife about the affair because he did not want to hurt her. He added that Miss Taylor organised and paid for his stag night and went to his wedding in Ireland. 'I drove over with Alison and Michelle. Michelle stayed at a hotel and B&B accommodation paid for by Alison and myself,' he said.
On 3 June last year Miss Taylor drove Mr Shaughnessy home after work. She asked if she could come in because she needed to use the lavatory. The couple found Mrs Shaughnessy's body at the top of the stairs, and Miss Taylor became hysterical. He said: 'She was crying and rushing about; after the police arrived she was sick.'
After Mrs Shaughnessy's funeral Miss Taylor tried to continue their affair. She met Mr Shaughnessy at a wedding in Ireland and asked if she could share his room because the hotel had overbooked. Mr Shaughnessy said: 'I agreed on one condition, that she just stayed in the room and that was it. She attempted to resume our old relationship but I was not willing.'
He said their relationship had ended a month before his wife's death. 'It was my mistake not to terminate the relationship and tell Alison about it,' he said.
He admitted Miss Taylor had never pressed him to leave his wife.
The trial continues today.