@Codex summoned me, so I'm adding my $.02.
Background - I've known a number of INFJs--male and female--over the course of my life. The most significant of those have been an on and off relationship for four years with an INFJ dude in college, two of my closest girlfriends in high school were INFJs, and my current relationship of ~6 months is with an INFJ 5w4 sx/sp. I'll limit my comments to my current relationship.
When it’s working – He and I are a team. We complement each other very well. We're both self-aware enough to recognize our respective "lanes" within the relationship, and have enough respect for the other to defer to them when we know that something falls more in their wheelhouse. Shared Ni facilitates this.
My partner is more innately imaginative than I am and also a lot more empathetic than I am as well. Knowing how to get along without making a situation antagonistic has always been a challenge for me, but being with him I know I can talk a situation over before having to act on it. Spending time with him has also helped me to develop my Ni, so I've become better at learning how to take a breath to think things through on my own, which is pretty cool.
He is without question acts as the "moral authority" for us. It's hard to explain, but he has a clearer idea of "who we are" as a couple, and what behaviors are and aren't in line with that. That ideal orients values, how we present ourselves and also the people we choose to spend time with. For the most part, I don't have a strong opinion on Fe things, but I value him enough to fall in on the things he feels to be important. Moreover, I know he prioritizes my wellbeing in these decisions, and thinking about image stuff stresses me out. I'm happy to let him do it.
For my part, I provide structure for the relationship. I joke with him that he basically outsourced all of his Te to me about two weeks into our relationship. I make sure we're accountable for whatever goals we set, and keep us moving towards attaining them. Sometimes that means planning. Sometimes that means poking him when he's disappeared into Ni-world to remind him that we made plans to begin with. I'm more comfortable with initiative and generally more outgoing, so when we're out and about, he basically lets me handle things and is cool with me doing the talking.
One of the best things about the relationship is how much I feel we learn from each other. I feel like I'm a better person and will likely do more in life with him than without him, and he feels the same way about me. As an ENTJ, I also highly value the fact that he's not afraid to push back if I overstep. One of my biggest issues with other introverts I'd been involved with was the constant feeling that I couldn't really go "all out" with them, or they just start to disappear over time. Te-doms are intense and even brutal at times, so it takes a certain kind of person to tell us to "No", and it actually slow us down. A partner with clear boundaries is pretty important for that reason.
In terms of understanding each other, we communicate very well for the most part. I can talk with him for hours and never get bored. He often surprises me and I love how imaginative he is. When we do have disagreements, we're able to talk about it and make a genuine effort to understand the other. Fe/Fi can be a challenge, but not in the way one might expect (I’ll get into that more in the next section). Overall, I feel we have a mutually enhancing point of view.
When it’s not working – There’s a couple of areas where we have challenges.
Balancing Dominant Te and Dominant Ni
The first, I’d say, is balancing the fluidity of being a Ni-dom vs the rigidity of being a Te-dom. These issues revolve with respective expectations on how and when ideas need to be translated into action.
As a Te-dom, follow through is a pretty significant thing for me. I’m not perfect at it, but I expect people to do what they say when they say they’re going to.
Ni deals with commitments like that a little differently. We’ve had a couple of situations where I’ve felt we’re committing to some set of plans whereas he feels we’re just discussing a set of plans and unholy hell breaks loose when I feel he’s not followed through on his word. We’ve had to be very explicit on both sides when we’re expecting action on something vs when we just want to share ideas.
Other times, he’s expressed frustrations when he wants to explore and be more spontaneous, and I’m trying to nail down time tables. The rigidity of extraverted thinking can be kind of a drag for him at times. He recognizes the value, but my idea of a good time can sometimes be overly structured, so he has to let me know when I need to put down the checklist, relax and have a good time.
Communication and being explicit about expectations has been helpful for us here, but it’s something we continue to work on.
Negotiating Fe vs Fi Priorities
He and I have an interesting symmetry, but definite points of departure when it comes to values. He’s libertarian and I’m a liberal for the most part, so our biggest fights have been about politics but tend to spill into other things. Fe often comes off as cruel to Fi, and Fi can come off as indulgent to Fe.
In my experience, Fe users can present their points of view as matters of fact rather than simply a function of their own experience. As an Fi user, I know when I feel a personal boundary has been crossed, it’s license to go all out. As a result of this dynamic, what he would consider an effectively impersonal conversation could occasionally get blisteringly personal on my end, and just escalate with neither of us wanting to back down.
Honestly, we haven’t found a good way to navigate this quite yet. I’m working on trying to stay connected even when we’re fighting so that I’m not going scorched earth on someone I care about because my feelings are hurt. For his part, he’s made a conscious effort to better understand my point of view to have more empathy for a perspective that he doesn’t necessarily agree with.
Another element of this is more interpersonal. I’d say for most Fi-users, a social “poker face” is without a question a learned skill. If I’m around someone I hate, then I’m not going to try...because I’m super petty like that. This is something that drives him insane. Conversely, him trying to placate idiots has a similar effect on me. I’d like to say that he’s made me nicer and I’ve made him more of a dick when he needs to be. At the very least, I’m more likely to give people the benefit of the doubt now than I used to be, and he stands up for himself more.
Advice for couples – Most ENTJs I know feel drawn to INFJs...almost compulsively. I think there’s a natural intuition that they possess something that we lack, and we have something to offer them in terms of the structure we provide.
As I’ve mentioned the biggest challenges I’ve experienced have come from Fe/Fi differences. Navigating those require ongoing communication and work, but aren’t insurmountable. This pairing is pretty unique in its potential for personal growth, because of the complementary strengths of each partner.
That said, it’s not some magical wonder pairing. If you respect the other person for who they are and are willing to recognize your own bullshit, you can end up with a pretty good thing on your hands.