Washington ( CNN ) -- Republican Sen. John Ensign of Nevada , who is under an ethics investigation by the Senate , announced Thursday that he will resign his seat on May 3 . Ensign had previously said he would not run for re-election in 2012 following revelations that he had an affair with a female aide who was the wife of another top aide , and that his parents subsequently gave money to the aides ' family . `` While I stand behind my firm belief that I have not violated any law , rule , or standard of conduct of the Senate , and I have fought to prove this publicly , I will not continue to subject my family , my constituents , or the Senate to any further rounds of investigation , depositions , drawn out proceedings , or especially public hearings , '' Ensign said in the statement . `` For my family and me , this continued personal cost is simply too great . '' Ensign : There are consequences for sin . Ensign has admitted to having an affair with Cindy Hampton , a campaign aide and the wife of Ensign 's former chief of staff , Doug Hampton . Investigators are looking into efforts by Ensign to assist the Hampton family by providing a nearly $ 100,000 payment to them , arranging lobbying work for Doug Hampton , and possibly meeting with Doug Hampton on a lobbying matter in violation of Senate rules . In February , the Senate ethics committee announced the appointment of a special counsel for the Ensign investigation . According to Ensign , the Justice Department has previously told him it would not bring criminal charges in the case . Read more about ethics committee action . `` I am gratified that , after extended investigations , both the Department of Justice and the Federal Election Commission saw no grounds on which to charge me with improper conduct , '' said Ensign 's statement Thursday . `` I was hopeful that , with the closure of these investigations against me the wear and tear on my family and me would soon be over . This was not the case . '' Ensign , 53 , was first elected to the Senate in 2000 . He previously was a veterinarian and general manager of the Gold Strike Hotel and Casino . After Ensign announced last month he would step down in 2012 , two House members from Nevada , Republican Rep. Dean Heller and Democratic Rep. Shelley Berkley , declared they would run to succeed him . Republican Dean Heller announces . Nevada Gov . Brian Sandoval , a Republican , is expected to appoint a replacement to serve the rest of Ensign 's term amid speculation that Heller would get the nod to give him an incumbent advantage in 2012 .
The Nevada senator is the focus of a Senate ethics investigation . Ensign previously had said he would not run for re-election next year . Two Nevada Congress members announced previously they will run for Ensign 's seat .