Heh ... NRE is "New Relationship Energy" ... It's basically what happens to you (emotionally) in the first stages after you and some new person fall in love. It's a euphoric experience. The whole world seems different. The Sun looks brighter. Colors are more vibrant. You feel like you want to shout to the world that you found this wonderful person you love, and they love you back!
The bad thing about NRE is it can blind you to your already-previously-existing relationship(s). It can cause you to neglect your "original partner" without realizing it. So during a spell of NRE, it's of utmost importance to shower your original/pre-existing partner with extra love and reassurance, as well as perhaps curb your enthusiasm a little when carrying on about the new person that you're in love with.
NRE can be a powerful catalyst for major changes in one's life. It's important to be really careful to make sure that the changes will be positive changes ... for all persons who are involved in the equation.
And that's why you got to beware of NRE. Hope that helps clear up any confusion.
Love means never having to say, "Put down that meat cleaver!"