Did Nicole Richie Cause Samantha Ronson and La Lohan's Break Up?

Could Nicole Richie be behind Sam and Lindsay Lohan’s break up? The on-again, off-again couple has split yet again, with one source telling E! that Nicole Richie’s friendship with Sam was the tipping point. “Nicole refuses even to be in the same room as Lindsay,” says the source, noting that Nicole invited Sam to a friend’s birthday party, but told her she couldn’t bring the girlfriend. “Sam went to the party, and it really upset Lindsay.”

After dining with Nicole last night, a source claims Sam finally decided enough was enough and ended her relationship with the troubled redhead .. .via text message! Ouch.