I'm in a 4-year relationship with another INFP, which I find very fulfilling! He comes across as a strong J sometimes but I think that this is a learned behaviour. I can be the same way. We understand each other, and we also both "understand that/what other people just don't understand", if that makes sense..? Our communication is good most of the time - we either have these great, in-depth conversations about things we both really care about, or when we're alone and snuggly we sort of just communicate through a series of grunts.
That's the beauty of it, I think. We understand each other to the extent that usually, nothing needs to be said, but we also are both interested in having the same kinds of conversations and exploring things in pace with one another. We like the same stuff and we have a lot of trust in one another, so we try new things together that are sometimes risky - we're scuba diving and fire performing partners! I don't really agree with working with your romantic partner, but I think that if we ever started a business together, we'd have the same ideas about how it should be run, and where it should go. But, we'd need someone else to implement it.
The challenge sort of comes up if the other person has done something that we find morally disagreeable, because you know what INFP's are like. To his credit, he is not the passive-aggressive one! He is very mature and a natural problem solver. I've never seen him lose his head, even when I'm flippin' out. But if he's doing something that I'm frustrated about or I find problematic, it cuts him very deep when I bring it up. He hates conflict and would prefer to avoid it which is usually good, but it can be cumbersome if there's something we really need to confront, and he's clammed up about it. We're also both emotional sponges, so when one of us gets into a foul mood, it invariably drags the other person down too. And, when I'm upset, he usually defaults to a "Don't be upset" approach or tries to cheer me up rather than just comforting me while I wallow, which is sometimes what I want, but usually not what I need.
If you ask the books, INFP/ENFJ is the natural match. I have also dated an ENFJ and can speak to that, a bit. It had the "fireworks", so to speak, but there were some big problems. I was always "his girlfriend", for one, because he was the extrovert. He also couldn't wrap his head around my need to be alone, to leave parties etc. If I wanted to be alone, he took that as meaning that something was wrong and hence if I insisted that nothing was wrong, he believed I was hiding things from him.
ENFJ's are also natural givers so the relationship did become one-sided. It's interesting because now in my INFPxINFP relationship, I sometimes catch myself slipping into the ENFJ role, and I was recently mistyped by a colleague as an ENFJ. I can see, now, how frustrating it must have been for my ex ENFJ partner, because he valued generosity and I valued fairness. I think that ENFJ/INFP relationships will always slip into that trap at some point, of one partner giving more (out of love) but then becoming resentful when it seems like it's not being reciprocated, or it's being taken for granted, meanwhile the INFP is basically unaware of this building tension until it's gone too far.
That being said, people are different. Me and that ENFJ were young; it may not have ended like it did if we had been more mature and more capable of confronting the issues that we had without being explosive. But, I think it's in the nature of both INFP's and ENFJ's to be explosive when tension is high and feelings are hurt, so it's a risk.
