Gaslighting aside, it’s certainly true that human memory is astonishingly fallible and thus largely unreliable, especially in emotionally-charged situations. My advice to anyone is: keep a journal. Write important things down. Not only will your journal permit a quick sanity check (“have I remembered X correctly?”) but it can also provide insight into one’s past many years later. I’ve kept detailed journals for both my children since they were born, recording the events of our lives, thoughts, feelings, etc. and every time I review these journals I’m astonished to read things I’d completely forgotten or, in some cases, misremembered significantly.