Barbara Bush nearly committed suicide in the 1970s during an episode of crippling depression sparked by her husband’s affair with an aide, a new biography reveals.

“She would pull over to the side of the road until the impulse to plow into a tree or drive into the path of an oncoming car had passed,” writes author Susan Page in “The Matriarch,” out Tuesday, a book based on hours of interviews with the former first lady.

“I really wasn’t brave enough to do that,” Bush said. “But that’s why I pulled over, so I wouldn’t do that, or I wouldn’t run into another car.”

President George H.W. Bush was long rumored to have carried on a lengthy liaison with personal aide Jennifer Fitzgerald, who joined his staff in 1974. She remained his gatekeeper while he served as vice president for two terms under Ronald Reagan. In 1988, when Bush was elected president, he moved Fitzgerald into a State Department job.

Bush and Fitzgerald both denied the rumors. “I’m not going to take any sleazy questions like that,” the president snapped when CNN asked him about it as he campaigned for re-election in 1992. “I’m not going to respond other than to say it’s a lie.”

But in a diary entry Page includes in the book, Barbara Bush seemed to think otherwise.

“My own opinion is that Jennifer really does hurt George,” she wrote in the 1980s. “His eyes really glaze over when you mention her name. She is just what he wants, he says and says the hell with it all.”

Both Bushes died last year — Barbara at age 93 in April, and George, 94, in November.