Baptist minister's son Benjamin Field, 28, entered into the "gaslighting" relationships with neighbours Peter Farquhar, 69, and 83-year-old Ann Moore-Martin in the Buckinghamshire village of Maids Moreton to scam them out of their savings and become the beneficiary of their wills, it is claimed.
Mr Farquhar, in various journal entries, describes his relationship with Field, with whom he was sharing a bed.
Details from the journal kept by Field were also among the various communications which were read out to the jury at Oxford Crown Court.
Mr Farquhar describes them as having an "intimate relationship" and also says "it was wonderful holding Ben in my arms".
He describes Field as being "so warm and loving" and notes that he brings him a cup of tea in the morning, the jury also heard.
Mr Farquhar also has a conversation with a friend who says he is concerned about the nature of his relationship with Field.
The friend does not press the issue further but Mr Farquhar states there was no sex involved in his relationship with Field.
Mr Farquhar was said to be "torn" by his sexuality because of his Christian beliefs, the court has heard.
By April 2015, Mr Farquhar notes that he is feeling extremely tired as it is affecting his ability to walk his dog.
He says that Field recognises the tiredness and they have a serious conversation about the future.
Mr Farquhar later recalled enjoying holding him in an embrace.
It is claimed that Field allegedly set out to make the elderly neighbours believe they were losing their minds - by spiking Mr Farquhar's food and drink with hallucinogens and neat alcohol, and writing "messages from god" on deeply religious Miss Moore-Martin's mirrors.
He had a sexual relationship with Miss Moore-Martin and is accused of enlisting the help of his friend, 32-year-old magician Martyn Smith, to help him make sure Miss Moore-Martin's death looked non-suspicious once she had changed her will, the court heard.
Miss Moore-Martin died of natural causes in May 2017 before Field and Smith could carry out their alleged plan, but prosecutors claim Mr Farquhar died from suffocation in October 2015 after undergoing a gay "betrothal" ceremony with Field.
A search of Field's home revealed a copy of the novel Young Poisoner's Handbook, a booklet entitled End Of Life and a copy of The Five Last Acts - a book about planning suicide.
Prosecutor Oliver Saxby QC pointed out that the poisoner who is the "primary character" in the Young Poisoner's Handbook is someone who "makes copious notes and records what he does".
Field has admitted defrauding Miss Moore-Martin of £4,000 to buy a car but denies recruiting his brother Tom, 24, to con the retired teacher out of £27,000 claiming it was for a dialysis machine.
Benjamin Field and Smith deny charges of 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.
But he has admitted four charges of fraud and two of burglary.
One of the burglary charges relates to a third pensioner from whom three antique rifles were stolen.
In addition, Smith, of Penhalvean, Redruth, Cornwall, denies two charges of fraud and one of burglary.
Tom Field, also of Wellingborough Road, Olney, Buckinghamshire, denies a single charge of fraud.
The hearing was adjourned to Monday at 10am.
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