I mistyped at SX 5w4 at one point. For a while, thinking that I mistyped at 5 was like "FACEPALM" but now, after letting many things settle in, I realize it really wasn't that ridiculous a mistype. I still have my "am I really a 5?" moments.
Once I came to PerC - getting out of the textbooks and finding what people were really like - then I mistyped at SX8. A lot of people on PerC suggested both 4 and 8 to me, as well as 7, but type 8 seemed most "me" since I have this voracious hunger about me. Once I learned the difference between lust and hunger, and how that voracious appetite for passion applies to sexual 4…. I mean.. this is making a long, complicated story short, but I .. am a 4.
It's like it isn't enough to just be close to someone. I savor every last corner of his dreams, his heart. At my most unhealthy, I need to become him or else I'm not close enough.
My ex is an SX-5 and one day he said to me, while we were messing around, "You have strong mirror neurons." haha. Apparently I was beyond turned on - just from turning HIM on. While I enjoy physical pleasure as much as the next person, the thing that really gets me off, metaphorically and physically, is when my partner is turned on. This might not have anything to do with enneagram, but for me, it's "yet another" example of introjection. I'm actually more healthy, in a better place psychologically, if the thing that turns me on the most, is something that I like, some expression of myself. But deep down, I mirror everything, down to his appetite.
4s identify with feelings, and feelings are ever-changing. I do have a strong sense of "who I am" but my feelings have formed that "sense of self" since i was a child, and in very deep passionate obsessions, those feelings can begin to over-ride previous notions of who I am, causing me to question everything I previously believed about myself. Deep passionate obsessions are personal transformation.
My 5w4 Sx/Sp ex is transformed by passionate attachments too, but it's more about how that person affects his mind and his way of understanding himself and the world. HE doesn't mirror the partner, but rather, seeks to figure them out, to understand them thoroughly. he doesn't re-shape his sense of identity, but rather, adds to his understanding of himself.
I mirror something more visceral. "Who he is." I can do this, in a visceral emotional way. I still do find myself loving a good mind-maze or trying to understand someone, but the basic, deep desire is feel his feelings, dream his dreams. My sx-5 ex was more… understanding my psychological underpinnings. It's not that different in action, as I am after the underpinnings too.. but I feel lost and disconnected if I can't relate to someone's feelings while he might feel lost and disconnected if he can't understand why something happened.