I think for me, my Fe development was a reactionary process. Throughout highschool, and beginning of university, I was a veritable prick (with a capital P). Or like my friends use to refer to it: OCS - Only Child Syndrome. And, then, in university, living in a dorm, for the first time having a roommate, and then, student housing (living with my best friends)....eye opener. Living with others (not parents who put up with a lot of my bs cuz they were my parents)...but, friends, having to navigate diplomatically, helped me tap into my Fe which had laid mostly dormant until that point.
Now, Fi, that is one that eludes me still. I am great at understanding other's motivations and feelings, but, when it comes to the realm of inter-personal, i.e., accounting for the I in a feeling exchange....is quite hard. I always seem to rationalize first.
Like I'll get a feeling of sadness, and rather than embrace that, the feeling of frustration/anxiety at 'why am I sad' overshadows the sadness itself....and I get lost within the loop of answering the why, and moving further and further away from the 'sadness' itself.
Or, if I can't still rationalize it away, I do the 'ostrich head in sand' technique...I ignore it because it's too convoluted to me, figuring out what I feel.
And, then, if it culmunates, I blow up in anger. My friends say that I only exhibit 5 feelings: meh, happy, excited, frustrated or angry.
The only way I tap into sadness, say, is if I watch a sad movie, or see a world event or see another's plith...i.e., channeled through Fe.
Only in extremes can I tap honestly into my Fi.... like a serious sickness in the family, where death was a distinct possibility...and even then my sadness gets overshadowed by anger. That time I kept up a stoic front in front of others and once away, and alone, I locked myself in my room and bawled my eyes out, until anger at my sadness inevitably took over, and I had destroyed/turned upside down all there was in my room. And, then, comes nonchalance. It's quite a battle, and one of my most active challenge, developing (healthy) Fi.
It's weird like being in a fog, sometimes. I KNOW what I'm supposed to feel/expected to feel in a given situation X, and it not coming frustrates me so that the frustration is more than the acceptance of the feeling. Like, I get frustrated not being able to show my Fi (when it's called for, like with the bf)...cuz I have a hazy feel of it, but, it's always on the periphery, and always just out of my grasp. Which creates a lot of tension because I'm charged with insensitivity (but, it's seriously not on purpose). I cheat sometimes, and actually get a script worked out of how I should feel/react in inter-personal matters through my F-friends. And, inevitably, some people catch on at the 'insincerity' of it all. Quite the issue.
I would love to know how ENTPs have developed Fi, actually (more than Fe). Esp. for ENTPs who score highly on T (like me).