I LOATHE the idea of a 'honeymoon phase' or 'new relationship energy' (NRE). I hate it like I hate the idea of men being less emotional than women (which, in case you didn't know, is empirically untrue). It implies a lie. It is true that some relationships are only good for the first 1-2 years. What is false is the idea that this shift is naturally occurring or inevitable. It is NOT AT ALL 'natural' to stop being excited about your lover. It's a sign that one or both of you need to develop your intimacy skills and/or personhood (or it may be a symptom of general lack of nourishment, or lack of common ground). The only thing that you have at the beginning that you can't have forever is novelty. If you crave novelty, just call it novelty. Stop acting like it is a part of every relationship or that every relationship has a 'honeymoon' and 'post-honeymoon' stage.
Reality can't dull anything that is real. I realized today that probably some people begin relationships with a fantasy of perfection. Starting out with fantasies and trying to see how much of each others' fantasy you can fulfill is not remotely appealing to me. I prefer to start out with nothing but questions and figure out what potential currently exists based on who each person is now (not who they want to be, not who the other person imagines them to one day be). Starting out with the idea of 'perfect' and working backwards to 'possible' seems inherently disappointing to me. Of course you're going to lose excitement that way -- but it's a loss of your ability to pretend, not an actual loss of something real. This is why in my relationships, I want to figure out if I have compatible values, goals, skills, and needs with a person BEFORE I invest deeply in them. Otherwise I'm likely to end up putting pressure on them to be what I want and need, and vice versa, and we're both going to end up hungry and drained.
Going back to the idea of NRE -- I don't believe in it. What people call NRE is actually IFE -- intimate focus energy. The giddy, excited, highly-nourished state is not caused by novelty, and does not have to dissipate with time. It gets associated with newness because in the beginning of a relationship there is a lot of fear and anxiety -- fear of losing this person, anxiety about making mistakes, etc -- and that gets channeled into focusing intensely on the other person (Abby coined the term "fear-spark" to describe this). You watch their every move because you're trying to figure out how to interact with them in a safely intimate way, and BECAUSE you're watching their every move, you're enchanted by them. Everyone is amazing if you look closely enough (well, everyone who isn't evil). Then, when you know them well enough to feel safely intimate, you stop looking so closely, and you stop noticing their amazingness. You take them for granted, because you can. And you call that the end of NRE and assume it is a natural phase of relationships. It's common, but it is NOT inevitable and it is NOT biological.