"Add into this now, starting in 2004, a very intense and emotional affair," Gwynn added.
For two years, they carried on their affair until Oefelein met Shipman and ended his romance with Nowak.
Gwynn covered the story extensively, penning the article, "Lust in Space," for Texas Monthly Magazine.
"If Oefelein thought Nowak was fine being downgraded from lover to just friend, he was delusional," Gwynn said.
"She was not fine with anything," Gwynn said of Nowak. "She was extremely in love with him."
A letter Nowak sent to Oefelein's mother around the time she was finalizing her own divorce, obtained by "20/20," may indicate how deeply invested she was in the relationship with Oefelein.
"I love him more than I knew possible," Nowak wrote. "Thank you very much for being there for me and us!"
"It was obvious that she believed that they were going to have a future together, until Colleen came along," Siegel said.
Shipman said she was oblivious to the back story.
That December, she accompanied Oefelein's family to watch as he rocketed into outer orbit, cheering his blastoff from the grassy banks of Cape Canaveral.
With the fury of that rocket blasting off, their love blossomed. Shipman said they kept in touch while Oefelein was in space through, at times, steamy e-mail correspondence. Oefelein even went so far as to call Shipman from the shuttle.
"I didn't recognize the phone number on the caller ID so I just let the voicemail get it," Shipman said. "It was him, and he was calling me from the space station. I didn't even know that was possible and I didn't answer it!"
The message, which Shipman shared with "20/20," was brief but in it, Oefelein made clear that seeing her was his first priority upon landing.
Had Oefelein decided to call his own apartment, Nowak may have answered.
According to police, she still had a key and the passwords to his computer. Sometime while he was in space, she let herself in.
"Lisa let herself in, and looked into his computer and saw not only some of the steamy e-mails but she also found a flight itinerary," Gwynn said.
Shipman and Oefelein rendezvoused in Houston after he returned from space and, according to Shipman, things couldn't have been better.
"It was a celebration. We were pretty much inseparable once he got back," she told Cuomo.
Shipman left to return to Orlando on Feb. 4, 2007. Little did she know that Lisa Nowak had left earlier that night in a small BMW. In her possession was Shipman's flight information taken from Oefelein's computer, a knife, a BB gun, rubber tubing, a hammer, pepper spray and directions to Shipman's house.
"I really thought for sure she was going to murder me," Shipman said.
Click here to watch Colleen Shipman take Chris Cuomo back to the scene of the attack, revealing harrowing details of her ordeal never before shared. Plus: The surprising end to the astronaut love triangle.