I relate so much with what you've said in your posts. I may be also a Sx/sp; at least, the description this page gives of Sx/sp 5's fits me perfectly:
http://ocean-moonshine.net/e1428573...er_op=view_page&PAGE_id=33&MMN_position=86:80
I think there's a core contradiction in all Sx/sp types. For example, on the one hand, what I really want deep inside is complete connection with somebody, like finding my other half. But on the other hand, my sp instinct prevents that to happen, because my natural reaction is detachment and building defenses against others. So I can have a one-night stand with a guy, no problem with that, but the next morning I just want to go away and don't see or talk with that person anymore. And that's because I don't trust people generally, I see them as potential dangers and, though I don't like isolation, I keep distances. I'm afraid I'll lose my self-sufficiency and become weak if I don't do so.
So, putting it in Freudian terms, I could say that my Ego wants intimacy with one person (that special person, may it be a lover or a best friend), but my Id tells me that depending too much on a person is dangerous and that I'm better on my own. It's really like self-sabotage.
Of course, being myself a 5, I'm not sure how much of this behaviour is due to sp instinct and how much is due to type itself.