Anecdotes from those who have either successful or failed INTP/INTJ relationships, with speculation as to what elements of life were most challenging and what elements of the two types were most complimentary. If you succeeded, what issues did you have to overcome and how did you do it; if you didn't, what was the biggest issue that sunk the relationship.
Prologue: I was in a long-term (4 year) relationship with an INTJ that imploded quickly after we got engaged (sometimes INTP have to have a bucket of cold water thrown on them to wake them up). Also it seems our genders are reversed and I think that may make some differences (due to gender role pressures, it's my belief/observation that INTP/INTJ females (like INFP/INFJ males) are more likely to be well-rounded i.e., have developed inferior functions). It may not really matter though so here we go:
The Good: Didn't tend to have huge values clashes. Neither of us were materialistic or put much stock in "life recipes" that prescribe how and when you do major life things. We spoke the "same language" being NTs = less work trying to explain where you are coming from. Superficially, our interests were similar but in the long run this is of very minor importance to long-term happiness. Of course, we both could nerd out on topics most people don't care about. Conversations were generally interesting/expanding, and I never got tired of his company (we would still be great friends if the relationship part had not happened, I'm pretty sure). Never had to deal with emotional outbursts or jealousy or other irrational behaviors. I could explain to him how he was wrong and he would accept it, and vice versa. Rarely fought.
The Bad: Major P-J clashes. He was uncompromising and harsh when his J was upset, and I was the one forced to accomodate by "becoming more J" (this just equals terrible stress for INTP, and honestly not a lot of success). I was slowly forced to become a sort of non-INTP (taking over all the procedural life tasks, e.g., cooking and laundry). If our relationship needed balance it felt like I was always the one who had to provide it. Terrible communication when it came to internal things (feelings). Fi's "just feel", which is weird to an INTP, while INTPs childish Fe can rub INTJ the wrong way (I just never brought it out). We both avoided serious relationship discussions. I kept a lot of my personality on "lock down" because I felt he would not like it (particularly, the creative, flighty side). He could not empathize well or show emotional support when I was going through a hard time (medical problems) and this contributed to a lot of distance between us. Both of us liked to make our own plans, neither wanted to let the other be driver. He asked me to marry him out of the blue - we had zero discussions beforehand, yet he had been thinking about it a lot.
That was kind of a stream-of-consciousness post, hope it is helpful. I don't think this pairing is doomed, but you need to both have developed emotional maturity and willingness/desire to engage in Fi/Fe.
