It starts off with small, benign things that are too small to make a big deal out of. Maybe I am an idiot for forgetting to do the dishes? Then they don't like your friends, your family is too judgemental and you need to respect whatever they say because your partner takes priority, how dare you not be completely committed to your partner?
I didn't really know what gaslighting truly was until I was already in too deep, but it involves eroding a person's self esteem, debasing their values and constantly putting someone down so they're constantly trying to think of anything they can do to keep their partner happy because that's what a good partner does. I think the tipping point when I started to question my relationship was when she punched me in my face on my birthday, kicked me out of the car and had to walk home 2 miles at 1am; I think I stayed in the relationship probably another 1-2 years after that because that's how effective it can be.
Oh and FYI they'll never actually take their mask off. Once I finally caught them red handed cheating on me, her mask "slipped" and she smiled for just a quick second. Then she doubled down and tried to say she can't live without me, its not what it looks like, and trying to seduce me, anything to sell the lie and never ever admitted the truth.