Once I cleared away and resolved all my emotional issues (depression, anxiety, ADD, C-PSTD, etc), all that was left was my core. I begun analyzing my core and it turns out that it is very different from other people. I don't desire to fit in or relate to anyone, not even you guys (I actually think a bunch of people here have simply been depressed forever).
I'm still not sure I am SPD, but I certainly have a lot of the traits, without the depression. One thing that makes me hesitate is that I have the ability to talk for 5-10 hours straight to a single individual (in person!) and neither me or the individual will feel drained. However I do not desire spending time with anyone, nor do I try to shy away from it when I am pulled in. This makes it that I consider myself to have "zero" friends while 10+ people might call me "friend".
Oh and the fear of engulfment is very much real, but at the same time I can let myself be engulfed if I enjoy it (like those very long conversations).
My version of SPD is very beautiful.