LEANN RIMES checked into a “treatment facility” after a cheating secret threatened to destroy her marriage!

The 30-year-old country singer sought treatment for stress and anxi­ety when she learned that her husband Eddie Cibrian was still in touch with a former lover, sources say.

Cibrian cheated on his first wife, “Real Housewives of Beverly Hills” star Brandi Glanville, with bit-part actress Scheana Marie – and the two women had an ugly confrontation on the Bravo series.

While the 39-year-old actor has cooled things with Scheana, 27, the former “CSI: Miami” star never lost contact with her, sources say.

“Their affair is defi­nitely over, but Eddie still has feelings for Scheana, and she’s tight with his good friends,” revealed an insider. “Eddie is very careful when he com­municates with her. He uses a member of their inner circle as an intermedi­ary, or texts and calls from friends’ phones.

“But someone told LeAnn, and she freaked out.”

Another close source told The ENQUIRER: “I think LeAnn feels very threat­ened by this girl. She went so far as to block Scheana on Twitter.”

The Grammy winner fell for Cibri­an when they were both still married, and pals believe she’s suspect­ed him of cheating for awhile.

“LeAnn called a friend a few weeks ago sobbing hysterically about Eddie going out,” di­vulged the insider.

“She was home for the weekend and he didn’t stay in with her. She was crying, say­ing that she was so worried about what he was doing.

“I think Eddie feels trapped. He probably just married LeAnn for the money, and there are only so many vacations you can take before you get bored with someone.”

Eddie’s cheating ruined his first marriage to Brandi, and she had a chance to confront one of her rivals, Scheana, while at the West Hollywood restaurant SUR with her “House­wives” co-stars.

“Brandi recognized Scheana – who was working there as a waitress – and straight out said to her, ‘You used to sleep with my ex-husband!’” recalled a pal of Brandi. “Amazingly, Scheana didn’t even deny it.

“Later on, Brandi told her friends, ‘I really do feel sorry for LeAnn. Eddie will never change – once a cheater, al­ways a cheater.’”

Meanwhile, LeAnn’s official story about going into the “treatment facil­ity” is that she sought help after being “cyber-bullied” by two women on Twitter.

“She’s even filed an invasion of priva­cy lawsuit against them, claiming they illegally recorded a phone conversation with her and posted snippets online,” said the source.

“While LeAnn may have been upset over the Twitter postings, the truth is that she had a meltdown when she found out Eddie was still talking to his former mistress.”