The seventeenth-season The Bachelor star and current Dancing with the Stars contestant is "putting his work first now, which means his relationship has to take a backseat," a friend close to the couple told Life & Style, according to RadarOnline.
"But no woman wants to come in a distant second in her fiance's life. Unless Sean is willing to put out his ambition and lust for fame and fortune, he's going to lose his chance with Catherine."
While Lowe and Giudici originally planned to settle down in Dallas, TX, the 26-year-old Seattle native and graphic designer moved to Los Angeles after getting engaged to support her fiance's current Dancing with the Stars stint. Lowe's experiences on television, however, are reportedly beginning to change who he is.
The alleged grounded family man "acts like a diva," a show insider reportedly told the magazine.
"When he goes to the [Dancing with the Stars] after-parties, he's always an hour late and brings the biggest entourage with him -- like eight people. No one else does that."
Likewise, a show source told Life & Style, "Fame has really gone to his head."
A friend of Giudici recently expressed how the bride-to-be is "bored and lonely" in LA because she isn't working and doesn't know anyone besides Lowe -- which is consistent with what a former The Bachelor contestant told the magazine.
"She's had a crying meltdown about everything she's going through," said the bachelorette, referring to how Lowe has allegedly been putting his growing career before his engagement and marriage plans.
The couple reportedly took a short trip to San Francisco together on April 4 following Giudici's breakdown, but Lowe had to rush back for dance training.
Although Lowe and Giudici initially planned to wed this summer, it now appears that may not be happening so soon after all.
"We don't have any concrete plans yet," Lowe told Life & Style. "It's hard to plan anything with my hectic schedule."