The former 'Hills' star was dumped by her NFL player fiance Jay Cutler last month even though they were busily preparing for a spring wedding next year and friends say Jay had been thinking about the split for some time.
A source told Life & Style: "She noticed a change in him. He suddenly became more supportive of her career. Up till then, he'd always talked about it coming to an end once they got married. It was like Jay knew he was leav¬ing the relationship and didn't want Kristin to miss out on great opportunities in Los Angeles."
Kristin - who dated Chicago Bears quarterback Jay for 10 months before they got engaged - recovered from the split by spending a night being comforted by pals heiress Nicky Hilton and model Alessandra Ambrosio at The Beverly in Los Angeles, where she was spotted without her engagement ring.
An onlooker said: "She was hanging out at a table with Nicky Hilton and Alessandra Ambrosio. She was telling friends how they called off the engagement."
The shock break-up came just a week after they held a party to celebrate their upcoming nuptials with Kristin tweeting: "Thx to all my amazing friends for making my engagement party a blast last night! (sic)"
Kristin has previously dated 'Laguna Beach' co-star Stephen Colletti and Brody Jenner, who she starred with in 'The Hills'.
Would you hand back your engagement ring if your relationship broke up?