The country singer - who now has a two-year-old daughter, Sunday Rose, with the actress - checked into a Clinic for drug and alcohol addictions just four months after their wedding in 2006.
But Keith, 43, who was hooked on cocaine and had been to rehab twice before, admits it was a turning point that brought them closer together.
During an appearance on 'THE OPRAH WINFREY SHOW', he said: "I thought, 'Surely let's give it a few years so we've got some solidity, because this kind of thing could tear us apart. This could just destroy us.' "
But Nicole and a few friends staged an intervention and forced Keith to get help, and those actions changed his life forever.
He said: "It was really a profound moment in so many ways.
"The way in which Nic' handled that moment was just perfect ... Everything was just designed, I believe, for that moment to fuse us together."
Keith - who claims it was his "love" for Nicole that made him determined to get clean once and for all - admits she has changed his life for the better.
He added "I look back now and realise Nic' has taught me so much and brought so much into my life and opened my eyes in so many ways ... This is the best place I've ever been."