Benjamin Field, 28, is on trial with magician Martyn Smith, 32, charged with murdering Peter Farquhar, 69, and planning to kill his elderly neighbour Ann Moore-Martin, 83, following a sustained campaign of "gaslighting".
Mr Farquhar died in October 2015, while Miss Moore-Martin, a retired teacher, died in May 2017.
Oxford Crown Court heard that Field, the son of a Baptist minister, told a friend he had a "struck a deal" to live with Mr Farquhar, a novelist and former English teacher, at his home in the village of Maids Moreton in Buckinghamshire.
Oliver Saxby QC, prosecuting, read extracts of chat logs recovered by police from Field's laptop in which he used the name "StAbleMan" and chatted to someone known as "the Big Unikitty".
In the logs, Field said he was living with gay Mr Farquhar, while also in a relationship with work colleague Nina Eriksen-Grey and having sex with other women.
The jury heard that Field's life was getting complicated as he juggled living with Mr Farquhar while also seeing Miss Eriksen-Grey.
Field and Smith deny murder, conspiracy to murder and possession of an article for the use in fraud.
Field, of Wellingborough Road, Olney, Buckinghamshire, also denies an alternative charge of attempted murder. He has admitted four charges of fraud and two of burglary.
Smith, of Penhalvean, Redruth, Cornwall, denies two charges of fraud and one of burglary.
Field's younger brother, Cambridge University graduate Tom Field, 24, of Wellingborough Road, Olney, is also on trial accused of a single charge of fraud.
The trial was adjourned until Wednesday.
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