The phrase "fickle mistress" refers to something or someone that is unpredictable, inconsistent, and unreliable. It often implies that this thing or person can change their behavior or loyalty suddenly and without warning. Full definition
Social networks are important, but ultimately they're not within your control: «Social media is a very fickle mistress,» Critchfield said. (realtormag.realtor.org)
But the Internet is also a fickle mistress when it comes to preserving the evidence for the future. (fortune.com)
But there are still a few guidelines that can help even the most luckless single out there, and if you're finding yourself bewitched by the fickle mistress of commitment this year, then take the following to heart. (relevantmagazine.com)