The intervention began at about 10 a.m. on St. Patrick's Day, March 17: Pat O'Brien's friend and attorney Ernie Del came into the entertainment anchor's bedroom with a shiny CD downloaded from the Internet. Del told his client he was immediately destined for detox. Soon O'Brien's longtime friend and coworker, Insider executive producer Linda Bell Blue, trooped in with several other high-level execs associated with the show. "They were all standing over my bed saying, 'You've got a problem,' " O'Brien recalls. Then they left him alone to listen to the voice on the CD. It was a string of drunken, kinky phone messages—which had found their way onto Internet gossip sites—O'Brien had left on a woman's cell phone. "My heart dropped. I thought, 'How in the hell has this happened?' "

Now, after a 40-day stay at an L.A. rehab facility to deal with an addiction to alcohol, O'Brien, 57, is assessing the damage. He was scheduled to return to TV with a double mea culpa: first a CBS special with Dr. Phil on May 4, then his syndicated Insider May 5. "When you hit the bottom with this disease, it's a real bottom, like being in a grave that hasn't been covered yet," he says. "I'm facing it like a man." In fact, when his friend Michael J. Fox called to check up on him recently, he even managed a laugh at how celebrity-news programs often depict troubled stars in slow motion. According to Fox, "Pat said to me, 'They're running me in slow motion on my own freakin' show!' "

In other words, a lesson learned the worst possible way. "I'm not going to drink again," says O'Brien. "On the other side of that door is hell. And I'm not ready to see that again." O'Brien denies rehab was a cover to dodge sex-scandal headlines but admits that yes, he left those voice mails, which invited an unnamed woman to join in group sex he hoped would also include his girlfriend, clothing and accessories designer Betsy Hoyt, 39. "It's my voice," says O'Brien, "but I don't remember making it."

Pressed to recall any other details of the day that ended with the phone calls, he smiles and asks, "Is this the History Channel?" Actually, it was March 13 in Manhattan. He and Hoyt had lunch. (He had filed for divorce from Linda, his wife of 30 years, in August 2004.) He "had a drink or two," he says. But somehow the day dissolved into "a drunken afternoon in a bar...[I] met a girl...too much champagne." Later there was also, he says, a little cocaine—and he made calls to the woman, he says, while he, Hoyt, the woman and a friend of hers were all at O'Brien's suite at the Four Seasons. He had gone to an adjoining room to dial the woman—"part of the insanity," he explains. "But it was a blackout night. No sex, just a drunken night that got out of control." He adds, "I didn't go through 150 experiences like that," but doesn't deny a history of partying.

There have also been claims of wild behavior that former colleagues say bordered on sexual harassment—one TV executive who encountered him said he was "an orgy waiting to happen"—but he says those are either false or exaggerated: "There are a million stories about me. I'm no angel." Still, he'd begun to sense that life was accelerating too fast. His marriage was ending as The Insider launched last fall, with alcohol fueling the ride. "It was something he thought he might need to get a handle on," says Michael J. Fox, "but each person has to find their own bottom." Hoyt says she knew O'Brien was struggling. "He worked around the clock. Pat would say all the time, 'What am I doing this for? I'm killing myself. I'm exhausted. I don't get to see [you or] my son.' " In the wake of the scandal, she told PEOPLE, "I'm seeing a different side of him. It's heartbreaking."

His longtime friend Linda Bell Blue says she never saw a dark side either. O'Brien routinely started his day by phoning her at 5:45 a.m. and was at work by 7. "The man I heard on that audiotape is not the man I work with every day."

In rehab, he says, he learned that "sobriety is not for sissies." In therapy he came to grips with a family history of substance abuse: His father, Joe, was an alcoholic, and his mother, Vera, "took a lot of pills." But the toughest moment for him was his first visit with son Sean, 17. "I'm his hero—I still am," says O'Brien. "I sat him down and told him the whole story. I may have not noticed my dad's problems, but he knows mine."

How will Act 2 play out? So far he doesn't miss drinking, he says. Over the April 30-May 1 weekend, he even mingled with the partying masses of the Coachella music festival in Indio, Calif., with Sean, who plays guitar in a band called the Naturals. But an uptempo, Insider-style wrap-up? Not yet. "He's a quieter person, more pensive," says Bell Blue. "He's got a structured outpatient program," which includes sobriety meetings. "There really is no cure for the disease," he says. And he knows those calls will haunt him for years. "There was one morning in rehab," he says. "We listened to Howard Stern on the way to the gym, and he was going crazy with the tape, mixing it with the Pope. I actually started laughing at one point. I thought, 'This would be funny if it wasn't me.' Maybe someday I'll laugh at it, like in 2012."

Tom Gliatto. Tom Cunneff and Vicki SheffCahan in Los Angeles