"We are taking a brief break so I can focus on myself," the 22-year-old tells E! News.
Ronson changed her relationship status to single on MySpace Monday.
On Sunday, the actress told Us reports she'd split from her DJ girlfriend were "not true" -- despite multiple sources confirming the opposite.
"This time, Sam means it," a source told Us Friday.
Samantha had security block Lohan from entering a party for sister Charlotte Ronson Friday night.
Afterwards, Lohan wrote to Samantha on Twitter: "So-you win, you broke my heart. now go away. i loved you"
On Saturday, Ronson had the locks changed on her Hollywood Hills home, where Lohan had been living for the past six months.
The couple dated on and off since May 2008.
More Photos: Lindsay and Sam in happier times