Does Ne work only when you are with other people. Do you feel you lose your Ne when alone? Well not completely lose it, but feels that Ne is stronger when you are with other people than alone?
To me, Ne is really the extraverted function like the name indicates. For inspiration, I need observations. I can't just sit still and come up with something. Going for a walk, going to the grocer's, doing chores... as long as I'm not staring at a blank screen, I can come up with the most wonderful stories.
If I've got an inkling of an idea and I want to work it out, the best method is doing it actively. Not just trying to think it through, but e.g. drawing, writing key words, even a calculation (yes, really... if I want a flat world with a sun orbiting around it, how will this affect the days and the seasons? By the way, the answer is "too much" - it wouldn't look anything like our world) can help.
Other people are the best! They provide not only great observation material but also feedback.
ENTPs are in their most "extraverted" ways if they are allowed to Ne (<- I love English, you can make a verb from every word), if they don't have to "socialize" in a traditional way.
Is it hard for any other entps to let go/ move on?
Depends. I think I'm fairly moderate in that aspect - remembering past friendships and relationships from time to time, feeling sad or thankful or both.
Any ambiverts here besides me?
If you look at the functions, I'm a clear E. (Ne first

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If you look at the usual E/I description, I'm more in the middle. I get drained by interaction as often as I get energized by it. And I'm not the only one. There have been E/I NTP discussions scattered among the forum, also in this thread. Lots of ENTPs experience draining interactions and the need to be alone. I suspect the difference lies in when we're allowed to let our Ne loose or not. If we're expected to socialize and talk about the kids, we can keep that up for a while (yay Tert Fe!) but we don't like it. Even now I've got a baby and I still prefer to talk about literature/science/...
A facebook status about the baby gets more likes than anything else - and then I'm totally puzzled. Come on, what's so interesting about another woman's baby? Aren't you interested in my book that's available now?
Any other ENTPs who don't know themselfs?
Puzzled by emotions when they mess up my thoughts, but on the whole, I think I know myself fairly well.