Interesting question and one I have thought about A LOT. The difference between love and intense feelings/nre or a crush.
I read a sign once that said that if you have feelings for someone for more than six months it's no longer a crush. ha, I searched and searched for any truth to it. never found any, not that it was a big surprise.
Any way to answer your question, I believe love is like faith. Deep down you just know, feel it with all that you are.
When you know someone really well, positives and negatives, and want to be with them regardless it's more than just nre.
These are all just opinions of course and a topic I could go on and on and on about, but it's the general idea.