Non-narcissistic people fall out of love.
It's okay to fall out of love and start seeing that the paths are parting and move on civilly.
What makes narcissists different and toxic is that they would do anything and would go to any lengths to make •you• say "I love you" only to take advantage of your feelings and abuse you in the most twisted and cruel way, and miserable and pained is how THEY love you.
ALL they do is take other people down, there's no other pleasure for them. And of course they will try to use your old "I love you" you said to them sincerely during their love bombing circus against you (very primitively and poignantly), implying you should owe your life to them as some sort of a pet no matter how they disregard you otherwise you are a judas. It's an oxymoron, really, but in their heads it's legit.
That is why "you can't win", their lies and manipulations are ridiculous and, sadly, non-stop.