In the TV show 'Lost Girl', Bo is a succubus, and succubi survive by feeding off the sexual energy of others, which can lead to death of the 'food' during the process.
Up until recently, Bo went a period of time without 'feeding' while in a monogamous relationship with Lauren, a human doctor who is aware of what Bo is and aware of the Fae. During which time, Bo started getting weaker - did Lauren not get harmed because Bo wasn't feeding at all?