The self-doubt rapidly dissipates once you withdraw all projections about that person who gaslights. It may not be a rapid process, but once you fully understand the "gaslighter's" attempt to be abusive, you can again breathe, and that feeling is pristine, rosy-cheeked, and unblemished!
The sadness exists that you had wished more from that person, perhaps having put them on a pedestal in your mind and value system. In the end, you finally understand that much of what they tried to teach you was sort of a "false flag", i.e., perhaps really good principles to teach to an Other. In the end, you may discover that the very essence of what they tried to teach you is their wish at the basis of their own darkness; however was nothing they actually possessed.
Your belief that they possessed a particular "brand" of integrity is likely projected by you upon them. For many reasons, that projection ends up being "awesome" news for you. Yet that is a discussion for a different time.
More important is the definition of "false flag".
While fairly military in meaning, it is a perfect fit for the person who, in your life, is the gaslighter:
Historically the term "false flag" has its origins in naval warfare where the use of a flag other than the belligerent's true battle flag as a ruse de guerre, before engaging the enemy, has long been accepted but the contemporary term False flag describes covert operations that are designed to deceive in such a way that the operations appear as though they are being carried out by entities, groups, or nations other than those who actually planned and executed them.Operations carried out during peace-time by civilian organizations, as well as covert government agencies, may (by extension) be called false flag operations if they seek to hide the real organization behind an operation.