became an overnight heartthrob after starring in Election
and the 1999 breakout hit American Pie
"It was nothing short of magic," says the actor, of his early stardom – something he quickly learned wouldn't last forever.
Klein slid into a battle with alcoholism that nearly cost him his career – and his life.
"I would have died, and I think about that every single day," the actor, 33, tells PEOPLE in an exclusive new interview.
After two DUI arrests
and a jail sentence
, the Nebraska-reared actor knew he had to turn his life around. Now nearly 19 months sober
, Klein opens about his struggles for the first time.
"It got to the point where I was a fragile shadow of the young man that came into this business," he says. "Today, I'm the luckiest guy alive."
For more on Klein during his darkest days, the truth about his relationship with Katie Holmes and his return to the big screen in
American Reunion, out April 6, pick up this week's PEOPLE magazine, on stands Friday