He agreed to pick up the slack and missed his Kuala Lumpur-to-Beijing flight, which then vanished and is presumed to have crashed with 239 people aboard.
The anguish and relief played out live on Twitter.
Reuters could not independently confirm whether the man, who goes by the Twitter name @KaidenDL, was indeed booked on the flight. Cylithria Dubois, in an emailed response to Reuters, said Kaiden was her "love and business partner".
"I am deeply chagrined by the attention that Kaiden and I drew upon ourselves with our tweets," Dubois wrote in the email. "At a time when the focus should be upon those aboard the ill-fated flight and their loved ones, I feel rather dumb speaking at all."
Dubois, whose Twitter handle is @cylithria, sent out a series of anguished messages on Saturday about the missing plane and how she couldn't contact Kaiden.
About 90 minutes later, he replied.
"@Cylithria can't reach you by phone. We missed the flight. Rory and I are OKAY Ria. I'm NOT ON THE FLIGHT RIA. I'M OK."
Kaiden did not respond to requests for comment. In his Twitter postings, he said he was angry at his girlfriend because "she'd gotten sick and I had to cover her. I was working on that, missed my flight to China. Grew angrier.
"But for the grace of God we'd be on that flight. Damn my ego. Instead of updating her, the office, I stewed," he wrote.