ROBERT F. KENNEDY Jr.’s wife has been abusing alcohol to cope with her fears that her husband has been cheating on her, sources have told The ENQUIRER.

That’s the tragic story behind Mary Kennedy’s recent arrest for driving while intoxicated.

On May 15, 50-year-old Mary was arrested after she drove her Volvo station wagon over a curb at a school in Bedford, N.Y. She told police she was there to pick up some people who had attended a carnival at the location.

Cops said she failed field sobriety tests and that her blood alcohol level was 0.11. The legal limit in New York is 0.08.

Insiders tell The ENQUIRER that the couple has been fighting over rumors that Bobby – son of the late Sen. Bobby Kennedy and his wife Ethel – has been unfaithful.

Ethel, 82, blew up when she first heard the cheating allegations two years ago, says a family insider.

"Ethel ended up giving him an old-fashioned tongue-lashing that lasted for more than two hours," divulged the insider.

"At the time, Bobby Jr. assured his mom that he loved Mary, but admitted that like any other couple, they had their problems.

"Mary, however, has never recovered and still fears he’s cheating.

"It’s led to domestic squabbles recently involving the police being called. The DWI bust has brought all this out into the open."

On ay 13, Mary called911 following an argument about the couple’s four children, according to Bedford Police Lt. Jeff Dickan. No arrests were made.

A family insider told The ENQUIRER: "They fight and yell a lot, and many times it gets very out of hand, very loud and many profanities are used."

Police also responded to a call from the Kennedy home on May 10, reportedly placed because of a dispute between children at the residence.

The entire Kennedy clan is now distraught over the growing family crisis – particularly Ethel, who is very fond of her daughter-in-law, says the insider.

Back in 1983, Bobby had a drug addiction and was arrested for heroin possession soon after he entered rehab.

"He cleaned himself up, but his personal life was never perfect," added the insider.

"Now he and Mary both need help."