For me, personally, I need emotional intimacy, mutual respect (my, this sentence is going to be long), mutual acceptance, good communication, physical intimacy and mutual attraction, respect for another's decisions, having a life (I dislike the 'over-clingy' types), mutual interests, acceptable economic background (I have no excessive expectations), a good attitude and a friendship . Don't be fooled by my 'T'.
I: 78% N: 88% T: 66% J: 44% Enneagram: The Reformer/The Investigator Global 5:RCOEI
I think that for NTs, more than any other type, mutual respect is a prerequisite.
Oh yes, for me this is far more important than any other aspect! I can function with anyone, as long as he (she) accepts and respects me, and vice versa. Since my original family members are all strong in "S" I have learned to adapt to that, and to being more outspoken. There are even situations when I become quite "J-ish" (I am a secretary in an association, locally, and in that situation I'm actually quite strict with rules+routines - but perhaps that's more because of the "F" people on that board who keeps on discussing how a board should be functioning, what we actually decided on our last meeting etc).
The only problem that I have found is when "J" people find it hard to accept and respect me when I'm being very "P-ish"...
My husband is INTP, and we function pretty well together. He leaves me plenty of space and freedom. Doesn't bother to give me flowers etc (and I wouldn't expect him to). He probably has a higher IQ than me (if possible ;-) , but that doesn't bother me as long as he doesn't speak of it - I freak out when people patronize me (for whatever reason).
I have been trying to figure out whether I'm actually INTP or INFP, I can see myself in both the "engineer" and the "daydreamer" types...!