Heidi Klum & Seal: It Was a Crazy Love Affair
01/25/2012 AT 08:00 AM EST
"They were just really great at keeping it private and putting on that 'perfect couple' front that everyone expected," says a Klum pal. But "it's actually been about six months that they've been working through some issues."
"It was a crazy love affair with highs and lows," says a source close to the couple, known for their over-the-top romantic gestures and lavish anniversary parties. "Most people can't sustain the highs when they're that extreme."
But even though they've decided to part ways, says one source close to Seal, "I believe they were madly in love."
For more on the real story behind Heidi and Seal's shocking split, pick up the upcoming issue of PEOPLE, on newsstands Friday