1) How does an ESTP use Fe?
I read on one profile that ESTP's can be hurt by people they have unconsciously come to trust. Is this like a sneak attack on Fe? Do ESTP's often not realize how much they care or trust someone until something threatens that?
This is a great question. In my opinion, if you wish to have relations of any sort with another person, you must trust them to a certain degree. You MUST trust your spouse. You MUST trust your friends. The degree of trust awarded should be commensurate with the magnitude of the friendship. If people violate your trust it is their error.
By default, I bestow a modicum of trust in all people, not enough to allow then to do me great harm, more of a gesture of goodwill. Trust is earned, so I pay attention over time as to how people use/abuse my trust. Those that perform poorly are ex-communicated from my existence, like that, gone. Those that are good stewards of my trust will be awarded more as life deems appropriate and their faith in me shall be repaid to epectations or better. That's just me.
We (ESTPs) are caused "pain" or more accurately "emotional discomfort" when someone we love/respect questions our character or does not recognize our presence in their life for whatever reason.
You are correct, sometimes you don't know how much you love someone until they do something hurtful to you. It is indeed an ambush, and from someone else, would mean nothing, as we would not have our "shields down", but from someone inside our "circle of trust" (I loooove DeNiro) an act of treachery is truly a miserable event that will illicit (1) pain, (2) wrath, or (3) both.
Despite being somewhat aloof and emotionally detached (think analyst, problem solver, superhero, not sociopath!) we do have feelings. When we are hurt, we are hurt deeply and re-act accordingly. Luckily, we get over things quickly, but pain is pain, and sometimes we succumb to that which we try to eliminate from our lives. ESTPs are fun loving good people, we hate pain, whether to receive or inflict it.
Now, I will say this, if someone screws me over with malice of forethought, literal pre-meditated vicious/hurtful things toward me, I will take vengenance. ESTPs are masters of hurling grenades back at people. We are friends to all men, women, and animals, but heaven help anyone who ends up on our shit list. It is a very, very bad place to be.
2) How does Ni show itself being the inferior function?
We are intuitive but we integrate it into our real-time cognition. We don't sit and ponder, simply because we don't sit. We ponder while on the move, and we are constantly moving. We analyze, decide, act and move on. Part of our analysis is intuition. How should this situation fold out? What is my gut telling me? These thoughts I have all day long, but I rarely think to myself "How do I feel about this situation?"
I think about what needs to happen, and once I decide on it I make my desired outcome manifest in reality however I need to within the realm of the law and ethical behavior. I will bend rules until they scream for mercy, and I will find any loophole necessary if I need to, but that's still playing by the rules, and rules were meant to be questioned as no code (EXCEPT the 10 Commandments) can possibly speak for all potential scenarios brought about in the human experience.
...And if you betray that, boy howdy, you better look out.
I will either denounce you to your face or find some way to subtly enact revenge or stab the knife in.
I cannot
stand someone betraying my friendship or sense of comradeship with them, even (sometimes it's something as simple as mocking me openly, or just stomping all over something I actually consider important). Sometimes I just let it go, but after awhile I can't take it anymore. It's like the ultimate sin, because to me my friends and equal relations are the most important aspect of my life, and I constantly strive to be charming and likeable (I actually see myself as vulnerable). But I'm not gonna go overboard on them, either. It's more like an eye for an eye, and I'll typically just turn the tables somehow, to level the playing field and get them to realize how they were wrong so we'll just go back to normalcy.
Bro, we are so alike it is not even funny. +1 to everything you wrote above. Awesome! Very well put!
As for Ni, the way I've heard it told is that function is able to predict how circumstances might play out under certain conditions or actions. I've also found that works best in the background because as I'm doing things my mind automatically generates the best action to take and when I do it without thinking, I instantly score with success. Other times I might predict what someone's gonna say, for instance, and I'll prepare my answers in advance.
I guess it'd end up being inferior if the ability to be reasonable was underdeveloped and an ESXP were to just do things willy-nilly without rhyme or reason and end up screwing up everything. That's my best guess, at least.
Yes, this too! Anything done willy nilly gets fucked up! That's why we're methodical, on-the-go, masters of reality. We have made plans, executed them, assessed their efficacy our whole lives, so no matter what happens, we have a battery of potential ways to address it via our gift of pulling from all that we've ever done and applying it to our current endeavor. This is how we learn, and we reinforce our successes because they feel good. Yeaaaah baby! I wanted "X" to happen, I predicted "Y" would yield the highest probability of success, I went for it, and VOILA! I got my way!
I should be ashamed for saying that maybe, but I'm not. I love winning. It's wonderful!
So it's a stalemate. I'm kind of getting bored with it and want to either 1) mix things up to get a reaction 2) end it and move on. 
