Well, I know this may seem far-fetched, but I havn't always been an ISTJ. In fact, I think I may have been an ENFP (or at least Exxx) at one time. Now before anyone starts poking fun of that statement (beat!) let me explain!
Yes, I used to be a risk taker, a real livewire. Then, due to a series of misfortunate events, I changed into an ISTJ, I vowed I would never be like the people who caused the misfortune on my family- the type of people who would take advantage of others just to make more money. The thin red line between right and wrong got etched into my mind. So THAT is why I am so attracted to the ENFP? They remind me of what I once was? I am always surrounded by Exxx's my whole family even extended family are Exxx and of course, all of my friends are Exxx.
However, none of my family are ENFP type, which intensifies my curiosity for said type. My best friend is the only ENFP in my "inner circle" that I know of, and we get along great! We keep eachother from getting down on ourselves. How much harder is it to get along with the ENFP female version? ENFP's truly bring the best out in me whenever I meet them, and I don't know why. (It must have something to do with their whimsical attitudes?) It's really strange, but I like it. That's the best I can explain it.
Anyways, what about the idea of the mutual friend?