• Tommy Sheridan and wife Gail
Mr McCombes said he had known former SSP MSP Sheridan for 26 years, saying they had "aligned" political values and barely passed a day without speaking to each other.
But the party's press and policy officer said he grew concerned that Sheridan had visited a sex club following a conversation with fellow SSP member Keith Baldassara in late 2002.
Following the conversation, he arranged to meet Sheridan to "discuss the information that Keith Baldassara had provided" and said Sheridan had admitted that it was true.
He said he was worried that the party would become "collateral damage" if the story was ever to leak out, as Sheridan had presented himself in public as a "squeaky-clean" family man.
He told the politician's perjury trial at the High Court in Glasgow: "I put it to him that he had attended a swingers' club, I believe on two occasions.
"His response was to accept it, to accept the fact that he had attended it."
Sheridan denies lying to the courts during his successful action against the News of the World in 2006, which followed the newspaper's claims that he was an adulterer who visited swingers' clubs.
He and his wife Gail, both 46 and from Glasgow, are accused of lying under oath during the action. They deny the charges.
Mr Sheridan won 200,000 in damages after the newspaper printed the allegations about his private life.
Mr McCombes said: "I wasn't having a moralistic position; my concern was that his public presentation was in sharp contrast with his private behaviour - that he had presented himself quite deliberately and consciously as a very squeaky-clean politician who constantly referred to his relationship with Gail - almost as the Daniel O'Donnell of Scottish politics.
"I believed his activities were more akin to the lifestyle of an English Premier League footballer than the leader of a political party.
"I was concerned that if this story was to appear in the media, then it would damage him and the party would become collateral damage and would be adversely affected."
But he said Sheridan had assured him that his visit would remain a secret.
He told the court: "He insisted that the people who were with him were 100% solid, they were close friends; there would be no way this information would ever come out publicly."
Mr McCombes said he discussed the allegations with Sheridan again in either 2001 or 2002, saying he was worried the story would leak.
But he said Sheridan had changed his position and denied that he had been there.
Mr McCombes said that, following the publication of the article in November 2004, he again met Sheridan at Mr Baldassara's office in Glasgow City Chambers.
He said the politician was adamant that he would sue the newspaper over the claims.
He said Sheridan was "very, very gung-ho about going to court, to lie in court, to commit perjury in order to win his case", adding that Sheridan also told him he thought he would be "destroyed politically" if he was named in an article.
Mr McCombes said he tried to arrange an "informal meeting" between Sheridan and some of his "closest friends and allies" to discuss a "damage-limitation strategy" at his flat, but Sheridan refused to come.
Mr McCombes said Sheridan then grew "contemptuous" and "abusive" of SSP members, adding that he was "shocked" by his attitude and it was followed by a "breakdown" in the previously strong relationship between them.
He said: "These were people who had given their lives, who had worked their socks off to get Tommy where he was.
"People who went back decades, people who supported him through thick and thin and his attitude was contemptuous and he refused to meet them."
Mr McCombes today became the 15th member of the SSP's executive committee to tell the court that Sheridan admitted going to the club during an emergency meeting of the party's top brass on November 9 2004, adding that there was "not a scintilla of doubt" about what he heard.
He said: "I was sitting beside him in the meeting. Mr Sheridan's voice is quite loud and clear. There was no possibility I could have misheard."
The indictment against the Sheridans contains three charges in total, two of which are broken down into subsections.
It is alleged that he made false statements as a witness in the defamation action of July 21 2006.
He also denies a charge of attempting to persuade a witness to commit perjury shortly before the 23-day trial got under way.
Mrs Sheridan denies making false statements on July 31 2006, after being sworn in as a witness in the civil jury trial.
The trial, before Lord Bracadale, was adjourned until this afternoon.