Gaslighting

I have been reading up on gas lighting but I'm still a bit confussed/?unsure on what it is...

My exN husband started complaining a lot about my memory... He was saying how frustrating it was for him that I didn't remember things and that it was having a huge effect on him and our relationship.. That is was a really serious problem I needed to seek help for!

I could never understand what he was talking about! Is this an example of gasnlighting?