Robert Bentley, a two-term Republican, stepped down as lawmakers began impeachment proceedings against him.
The 74-year-old former Baptist deacon and dermatologist was last week defying calls to step down, including from leaders of his own party.
He had also “encouraged an atmosphere of intimidation” to hide the scandal, according to the findings.
In other texts between the governor and Mrs Mason, one from her phone said: “You handsome, wonderful, amazing, delicious, funny, sweet man.”
Mr Bentley, who was first elected in 2010, replied: “You are wonderful my sweet love. I love you.”
In another exchange, the two discussed their desire to elope.
According to the findings, the governor also mistakenly sent his wife, Dianne Bentley, a text message that said, “I love you Rebekah”.
In March 2014 Mrs Bentley secretly recorded an explicit phone conversation between her husband and a woman he addressed as Rebekah.
“When I stand behind you,” he is heard saying in a recording that was leaked to local media, “and I put my arms around you, and I put my hands on your breasts, and I put my hands (unintelligible) and just pull you real close. I love that, too.”
Mrs Bentley filed for divorce in August 2015, saying the 50-year marriage had suffered an irreparable breakdown.
Mrs Mason, whose husband also worked for the governor, resigned in March last year as the scandal emerged.
Mr Bentley’s resignation does not draw a line under the scandal.
On Monday afternoon, he had his mugshot taken by Montgomery County Sheriff’s Office on two misdemeanour charges of campaign finance violations linked to the alleged affair.