Lindsay Lohan, Samantha Ronson Split

Lindsay Lohan and Samantha Ronson have split again, a source tells UsMagazine.com.

"This time, Samantha means it," the source tells Us.

According to MSN Wonderwall, the couple, who publicized their relationship in May 2008 at the Cannes Film Festival, got into a fight over the weekend at a party Ronson threw for her sister at West Hollywood's Bar Marmont.

"[Sam] told security to look out for Lindsay and block her from getting in," a source tells Us. "Lindsay, of course . . . booked a room at [the hotel] Chateau and fully intended to crash the party and make a scene."

Bouncers kept Lohan from entering the party, another source tells Us.

"She was heartbroken, but Sam did not want Lindsay entering and causing a scene and ruining [her sister's] night," the source says.

However, a source close to Lohan insists it was the Ronson family who stayed in a room below her at the Chateau Marmont and "blast[ed] music and would not let Samantha leave the room to meet Lindsay."

On her Twitter page, Lohan posted to Ronson, "PLEASE leave me ALONE. and stop staying in the room below me, you've woken me and my mother up. go to bed. keep cheating u win."

Lohan denied there was any drama, despite multiple sources, witnesses and her Twitter pages telling Us otherwise.