The break-up with DJ Ronson "came out of nowhere," Lohan said, stemming from a violent blowout she and Ronson, 31, had earlier this month.
Lohan said she didn't realize she and Ronson were done for good until Ronson "disappeared" after the fight.
"I had no idea what was going on. I just hadn't seen her in, like, a week," People reports Lohan spilled on the show.
Lohan also said she had no idea why the Ronson family filed a restraining order against her and that she's been nothing but supportive of Samantha's friends and loved ones.
"I've never done anything for people to assume that I'm dangerous," Lohan tearfully as she choked up on the show.
As Lohan deals with the break-up, she's reportedly wasting away -- doctors say the starlet weighs a dangerous 95 pounds and is only getting thinner.
"There are signs of muscle wastage, clearly her bones are protruding and she looks quite rigid," Dr. Kent Holtorf, director of the Holtorf Medical Group in Los Angeles, told Fox News. "She looks like skin and bones at this point, Lindsay clearly looks malnourished and unhealthy for her frame."
The 22-year-old actress bonded over her sadness with host Ellen DeGeneres, who's had her own share of break-up drama -- her rollercoaster relationship with Anne Heche was tabloid fodder for the better part of 2000.
DeGeneres said she "hibernated" for awhile after the break-up and that Lohan could benefit from some similar time out of the spotlight.
Lohan also denied charges of infidelity, telling Ellen that she's never stepped out on Sam or any other partner.
"I don't believe in cheating on someone," she said. "I watched my father do that to my mother my entire life, so no."
The devastated Lohan said on "Ellen" that she's hopeful for a reconciliation with Ronson, when both are "fully in the right place."
"I love her," Lohan said.
The episode of "Ellen" is scheduled to air Thursday afternoon.