I hear you girl! I know exactly how you feel. I beat myself up whenever I let someone down...but in the end that is really my problem. Here are my thoughts...said with nothing but love:
I think it is entirely possible that when the istp said, "You're wrong. Apologize." It stung becuase you think his assesment is RIGHT. For example if he said, "You're a caterpillar. Apologize." You wouldn't be upset...you would think he was nuts, becuase it is so far from the truth. The bristling is simply a defense mechanism becuase he is hitting a place that hurts.
The real question is not who is right and who is wrong, but why does it hurt? As an ENFP (as is true with ENFJs), we tend to have issues understanding or aknowledging our underlying NEGATIVE feelings. So how do you feel (never mind what everyone else is feeling about you). Do you feel guilty? Do you feel rejected by your friends becuase of their response? Misunderstood? Drained? Do you feel like a disappointment? Figure out what YOU are feeling and then ask yourself why you are having those feelings.
I feel very guilty when I let people down, but I am learning (and it is work) to talk to people about things and to set boundaries. Its REALLY, REALLY hard to do at first, but then it gets easier. Maybe you need to talk to your friends about their expectations of you and explain how it makes YOU feel to feel like you have to be everytig to everyone and then change their expantancies.
I have been doing this for the past year and I had some really rough patches with some of my friends (becuase they resisted the changes) but I had to do it for my sanity and I kept telling myself, if someone doesn't want to be my friend because I won't cater to their every whim, is it really a friend worth having? But I have to reiderate, it really is about getting in touch with your own emotions and needs and then CLEARLY articulating what you want and why you want it to the people around you. As NFs we are kind of "mind readers" at times...most people aren't. Give people a chance to succeed in making you happy by telling them what you need from them.
Life is MUCH easier for me now than it was a couple years ago (although I am still a work in proccess), but it has indeed taken a lot of hard work to get here.
Good luck. I know how you feel