Colin Craig has given more details of how he saw the relationship develop between himself and former press secretary Rachel MacGregor while they worked together.
Ms MacGregor worked as press secretary for the then Conservative Party leader between 2011 and the 2014 election, but resigned two days before polling.
She lodged a sexual harassment claim and there was later a confidential settlement.
Mr Craig is suing Ms MacGregor for defaming him on three different occasions including in details she gave Jordan Williams from the Taxpayers Union about their relationship.
Ms MacGregor is counter-suing Mr Craig for defaming her four times, including in a booklet sent to 1.6 million households.
Mr Craig continued to give evidence today, and said the pair became close friends, with Ms MacGregor responding positively to his letters to her.
"Rachel told me the letter was so meaningful that she kept it beside her bed and that it was a constant encourage for her to read it. Having received a second very positive response to a letter, this encouraged me to write further letters in future."
He also addressed the accusations against him - one of the defamation actions against Mr Craig is around comments he made in a booklet he sent to around 1.6 million households called Dirty Politics and Hidden Agendas.
"To the best of my knowledge the booklet is true and it was certainly my true belief at the time I published it to defend myself against Mr Williams, Slater and Stringer. I didn't publish the booklet to attack Ms MacGregor and I don't understand why Ms MacGregor is suing me for what I published in the booklet. The booklet was focused on the actions of Mr Williams, Mr Slater, and Mr Stringer."
Mr Craig said allegations Ms MacGregor had made to Mr Williams were later summarised and published on a blog. These form part of his case against her.
He denied any of the allegations were true and said they had tried to paint a picture of harassment.
He dismissed Ms MacGregor's evidence that the claim was a way to punish her.
"As I have already explained I could have published very personal details damaging to Ms MacGregor if I wanted to, but I chose not to do so. Once parts of my communications were released I could have released her's in response, but I chose not to do that either."
Mr Craig filed the defamation case in November 2016 but said he had not planned to go through with it.
"I only filed the claim to preserve my position and in fact by Christmas 2016 I had decided not to proceed with it and therefore had not served it. My understanding was that if it was not served within a year it would become defunct."
He said he was "shocked" when media found out he had filed proceedings later in 2017 and it was only when Ms MacGregor filed her defence and counter-claim that they were initiated.
"I do not consider that this proceeding is in the interests of either party. I've offered to discontinue on six occasions. On five of those occasions I offered to contribute to Ms MacGregor's costs"
He said the last offer of $30,000 was made on the eve of the trial.
Under cross-examination, Ms MacGregor's lawyer Hayden Wilson was critical of Mr Craig's serving of the lawsuit.
"You're aware that there's an obligation in the High Court rules to serve proceedings promptly once they are filed?" Mr Wilson asked Mr Craig.
Mr Craig said he did understand that now.
Mr Wilson put it to him that if Ms MacGregor had not found out about the proceedings and filed a counter-claim when she did, it could have been too late.
Defamation cases have to be brought within two years after the event.
Mr Wilson also questioned Mr Craig about why he hadn't disclosed that he had filed defamation proceedings when he cross-examined Ms MacGregor for two days during his trial with Cameron Slater.
"I didn't for the same reason that I never advised anyone about it because it was my view by then I wouldn't take them forward," Mr Craig said.
Mr Wilson also went over letters Mr Craig sent Ms MacGregor and asked him to read parts to the court, including one where he expressing a desire to kiss her and "go further"
He put to Mr Craig that some of what he wrote wasn't appropriate for an employer.
"Do you accept that they're deeply inappropriate for a person who is an employer to send to an employee, however good their friendship?
"No, again you're putting it in the context of the employer, employee or a contractor. These were written because there was a very, very deep and close friendship between us."
Earlier, a judge ruled Mr Craig can go ahead with one of his main defences against defamation after he forgot to include it in his case.
During the first day of proceedings Mr Craig, who is representing himself, sought to add an argument of truth to his defence against her allegations, saying it was an error not to have included it originally.
"Obviously I argued in my opening submissions on the grounds of truth and my friend's pointed out that's not within my pleadings ... that's a mistake on my part and it ought to be in my pleadings."
There are a number of defences against defamation, including whether what is said is true.
He said it was an "oversight" and he had not realised Ms MacGregor's lawyers had pointed that out in their submissions.
"I don't know that it does create prejudice as such and a lot of my evidence goes to the defence of truth in any case."
Mr Wilson, opposed the change.
"Mr Craig is not a man who is new to defamation proceedings. He has never pleaded truth in this proceeding to date.
"I'm a little at a lost that when we served our opening which was explicit, that Mr Craig didn't realise this was a mistake at that point.
"It's a substantial amendment by any means to introduce a new defence after the opening of the claim when there's been no new information that may give rise to it.
Justice Hinton gave counsel until this morning to consider the matter.
This morning Mr Craig directed her to part of his submission in which he said his "main defence" was truth.
"Oh, I see your main defence is that the allegations you made were true. Your main defence is just not pleaded," Justice Hinton responded.
She granted his amendment.
Cross examination of Mr Craig will continue tomorrow, with the case set down for two weeks.