The former 'Hills' star and the 'Dancing With The Stars' professional - who has previously been linked to British pop star Cheryl Cole - were always "casual", but Lauren has decided to call time on their relations.
A source told Life & Style: "The relationship reached its peak. It was always casual. She had fun with Derek - he used to send her cute texts and sing to her - but she always kept her options open."
Another source noted Lauren considered Derek a rebound after breaking up with her boyfriend of three years, Kyle Howard, in June.
The insider added: "This was a rebound that wasn't going to last. Derek never thought it would either."
In September the pair were seen enjoying each other's company at the Sayers Club in Hollywood, where the pair could not take their hands off each other.
An onlooker said: "They were close to each other. He had his arm around her waist. They were dancing and also holding hands. Definitely playful and flirty."