I've been in two relationships with narcissists...exH who was diagnosed with NPD, and I believe my ex boyfriend was one too but I ended that relationship after 7 months when I was convinced enough by the patterns of behaviour.
I'm not really totally at peace yet with either relationship if I'm honest. I'm 5 months into counselling though and it's incredibly helpful unpicking why I ignored red flags and so on. The best way I explain it to myself is that I fell in love with an act, a con, a dream. But as someone else has already said, that doesn't take any validity away from the depth of that feeling just because these men were fake, my feelings weren't.
I'm also seeing that as painful as these relationships are, they can be a gift because you learn SO MUCH about yourself. You can't unsee or unfeel certain things anymore; you spot signs and you are more self aware. Yes you lose innocence to a certain degree, but it gives you the opportunity to live a fuller life once you've healed.
Narcissists are very good at spotting what matters to you most during the love bombing phase (when they do their research on you) and they hold that up as a virtue but when they start to devalue, that's the things they will use to hurt you with....because they know what makes you tick. For me it was my children and career....both of those are the things most important to me. And both were eventually criticised and ridiculed.
It's the most insidious relationship to be in as it invades your soul but...they choose the things to tear you down that secretly they envy you for. Remember that the person they make you out to be at the end is really the person they are inside. They will never be anywhere near as vibrant, strong and courageous as you.