LAS VEGAS -- The sex scandal engulfing Sen. John Ensign deepened Wednesday after his former mistress's husband revealed new details about the relationship, saying the senator paid the woman over $25,000 in severance when she stopped working for him.

Doug Hampton also provided a letter to the Las Vegas Sun newspaper that he claimed was a handwritten apology from Ensign to Cindy Hampton, a former treasurer for the senator's campaign committees. "I used you for my own pleasure," the letter reads, later adding. "Plain and simple it was a sin."

The letter and interview with the newspaper mark another embarrassment for Ensign, a 51-year-old Christian conservative Republican who abruptly came forward last month and confessed to the affair. In addition, a severance payment could pose campaign finance and ethics issues for the Republican if the amount was not disclosed.

Neither Ensign's spokesman nor his attorney returned a call seeking comment.

Hampton told the newspaper that he learned of the affair between his friend the senator and his wife when he discovered an incriminating text message. He also detailed a February 2008 meeting in which he, Republican Sen. Tom Coburn of Oklahoma and others encouraged Ensign to end the affair, as well as the working relationship with the Hamptons. Hampton said Coburn and others tried to encourage Ensign to compensate the couple and help them relocate.

"These men were the ones that said, 'What we need to do is get Doug Hampton's home paid for, and we need to get Doug Hampton some money. We need to get his family to Colorado,"' Hampton said in the interview, according to a transcript obtained by The Associated Press.

John Hart, a spokesman for Coburn, would not comment directly on the specific advice that Coburn gave Ensign.

Coburn "did everything he could to encourage Senator Ensign to end his affair and to persuade Senator Ensign to repair the damage he had caused to his own marriage and the Hamptons marriage," Hart said.

Doug Hampton said the men encouraged Ensign to write the letter of apology. The senator later told his mistress to ignore the note, Hampton said.

In the Feb. 2008 letter posted on the newspaper's Web site, someone signing their name "John" says he takes "100 percent responsibility for my actions." "God never intended us to do this. I walked away from Him and my relationship with Him has suffered terribly," the letter reads.

Doug Hampton also worked for Ensign as a Senate aide. He claims his wife received the payment as severance when she left her position in May 2008. Both men say the affair continued until August 2008.

The two families are longtime friends. They both live in the upscale suburbs west of the Las Vegas Strip and their children have attended the same school.

Ensign's office has acknowledged helping Doug Hampton get work once he left the Senate office, first as a consultant and then as a lobbyist for an airline run by an Ensign contributor.

Through a spokesman, Ensign has accused Doug Hampton of recently making "exorbitant demands for cash and other financial benefits."

Hampton said in the interview that attorneys for the men have been in negotiations over "millions" in possible payments from the senator. Ensign, through his spokesman, has refused to answer questions on whether any payments have been made.

Campaign committee records do not show a large payment to Cindy Hampton when she left her job. If the payment occurred, it could present a possible campaign finance disclosure violation, campaign finance attorney Kenneth Gross said.

The nature of the violation and penalty depends on "how the senator chooses to characterize the payment," he said.

"It's an entangled situation and like most circumstances the devil is in the details on whether its described as gift or income, and whether there are tax or campaign disclosure laws implicated," Gross said.

Earlier reports of the possible severance prompted a Washington watchdog group to file a complaint against Ensign with the Senate Ethics Committee.

Citizens for Responsibility and Ethics alleges Ensign may have violated ethics and campaign finance rules by failing to report the payment to Cindy Hampton as an in-kind contribution from his leadership political action committee.