The Welsh rugby player is believed to have broken up with the 24-year-old after driving to meet her for a romantic meal in London this week.
"Carianne was really looking forward to the meal and he just dropped a bombshell," an insider told The Sun. "She's furious and thinks he's really vain."
The couple got together after Henson chose her over 24 other girls in Channel 5's debut series of The Bachelor, which aired last year.
"I feel so lucky to have found you, you're so unique," he said when picking her in the show's October final. "Please give me the opportunity to make you feel special.
"Let me be your best friend and give me the opportunity to make you happy for the rest of your life."
Henson was previously engaged to Charlotte Church, but the couple ended their long-term romance in May 2010.
The former couple have two children together, Ruby, 4, and 3-year-old Dexter.