I agree that you know it's Love when you have seen the best and the worst of each other and not only do you still want to be around that other person, but it actually makes you love them more.
NRE dissipates in a hurry when the going gets tough and there's no real love to fall back on.
My love and I have had our share of troubles these past several months yet we still remain committed to each other. That's what assures me that the love is real.
It is the best of both worlds, as Lovefromgirl also states, I still get butterflies when I know we are about to see each other. And the funny thing is, we have determined that the longer we are apart, the stronger those feelings get, distance/absence really does make the heart grow fonder.