Nevada Senator John Ensign announced on Thursday his resignation from the Senate, the AP reported.

The two-term Republican who opposes gay rights, including giving gay and lesbian couples the right to marry, acknowledged in June, 2009 that he had a nine-month affair in 2008 with Cynthia “Cindy” Hampton, a former member of his Senate campaign staff. He also admitted having helped her husband, Doug Hampton, a member of his Congressional staff, get lobbying work.

The 53-year-old Ensign, who was considered a rising star of the GOP and possible presidential material, is under investigation by the Senate Ethics Committee.

Ensign, however, didn't admit to any wrongdoing – “I didn't break any of the ethics rules. I didn't break any of the laws. I didn't do any of those things” – in announcing his departure.

“I just came to the conclusion that I couldn't put my family through it,” he said.

In 2004, Ensign urged Congress to pass a constitutional amendment banning gay marriage, saying “Marriage is the cornerstone on which our society was founded.”

Ensign also chided Idaho Senator Larry Craig after his arrest in a Minneapolis men's room for lewd behavior. He called Craig a “disgrace,” and called on him to resign. Craig served the remainder of his term but never admitted being gay.

But while Ensign scores a zero on the Human Rights Campaign's Congressional Scorecard, a measure of a lawmaker's support for gay rights, his likely replacement, GOP Rep. Dean Heller, won't improve Nevada's score. He also received a zero.