Usually done dishonestly, by people who are incapable of functioning without an audience giving them constant affirmation that they exist. Often indicates emotional immaturity and narcissism.
Bed-warming is most effective online, where real details of the bed-warmer's life and circumstances are not visible.
"Dude, she's bed-warming. Don't take it personally. Or at least don't take it seriously."
"Do you like crowds? Because you're in one. He's bed-warming you and at least six other people."
"Run away. Bed-warmer. And married. And a pathological liar looking for a therapist/mommy/housekeeper/bill-payer/way out of the marriage."