I’m an INTJ who has been in a relationship with an INFP for 7 years, so I think I can give some advice to fellow INTJs. Obviously, these are just one man’s personal experiences so don’t take them for granted, think for yourself and feel free to disagree with me.
If you are an INFP reading this and find something I mention a bit too harsh, please know that I only wrote this comment because I think it can be beneficial to you/your partner and that I think you guys are among the most wonderful creatures on Earth.
If you are an INTJ: This is a long comment with personal anecdotes so if you do not care about those, here are my principles, check these out and you can stop reading:
1. Learn to accurately assess whether they are already solution oriented about a problem or still at the “feelings stage”
2.Learn to plan spontaneity
3.Always be nice to the people they love the most even if you don’t like them
4.If you suspect he/she will want to talk about emotions play out the conversation in your head a couple of times, jot down your thoughts and practice your responses
5.If you want the relationship to succeed you simply have to make him/her a priority, there is no hack around this one.
1.
For me, the emotion I feel most intensely is anger. When a problem occurs, 99% of the time I deeply feel anger that this problem is messing with my plan, so I channel the energy that anger generates into designing a solution to the problem.
The emotion my INFP felt most intensely is insecurity. When a problem occurred, she would start second guessing herself, always thinking that it was somehow her fault, and that she was never good enough. This feeling of insecurity had a paralyzing effect on her and would always include a period of inaction, or a “feelings stage”, while she wrestled with her emotions.
As I found there’s nothing you can do with this, except being there for her while her internal storm passes. Giving her the solution to the problem doesn’t  help, neither does bringing up logical arguments that it’s not her fault, that she’s good enough, and that it’s probably not the end of the world.
INFPs are smart and they’re great problem solvers, so once they are finished with all these feeling things they will probably figure out the solution on their own. Independent as they are, they probably wouldn’t want you to solve their problems for them anyway. Just be there as a lighthouse amid their stormy sea of feelings, and maybe help with implementation details once they are solution oriented.
2.
This might sound paradoxical, but you can act like you’re spontaneous without actually being spontaneous. You can achieve the illusion by designing and planning. For example, there is nothing that would light up my INFPs day as much as small little surprises like picking her up from work unannounced with some flowers, donuts or something like this. These surprises don’t actually have to be random, it only has to seem that way. Indeed, most of these things I planned out weeks before, otherwise I wouldn’t actually had time to do them. The point here really is to not reveal this, but to say something like “I just couldn’t focus on work and had to see you” (I can always focus on work). This can generate amazing psychological effects in them. While I strongly discourage any kind of untruthfulness and advocate complete transparency, I think small positive lies like this one are acceptable for the sake of a long term relationship.
3.
There were many people I didn’t like in my INFPs family. This was nothing personal, I had objective reasons for not liking them. They made financially unwise decisions, had mental health issues they weren’t addressing, and so on, each of which negatively affected my INFP and therefore negatively affected me. For a long time, I would tell these people how to solve their problems and I would also deliver criticisms both to them and to my INFP. This is certainly not a great move. INFPs I believe are fiercely protective and not very objective about their loved ones and would protect them in an argument even if they know that you are completely right. They also tend to take objective and well-meaning criticisms as personal attacks. So… how do you solve this one? First, try not to be rude to these people, even if you want to slap them in the face for the dumb and ignorant decisions they’ve made. Second, help your INFP learn how to remain balanced and calm, and help him/her understand that he/she is responsible for his/her own happiness, and not responsible for the happiness of other people who are grown up independent people.
4.
In an INTJ INFP relationship, I think the difference in functions manifests most strongly in discussions about emotions. INFPs can talk at great length about their feelings and can deliver a well-composed analysis of those feelings. If after a 15-minute monologue about their inner life the most you can say is “I feel sad” or “That’s great” they will feel that you don’t care/don’t pay attention to them. The fact that you indeed listened intently to every word they said is irrelevant.  So accept and explain to them that even though you might feel as deeply as they do, you are unable to articulate these feelings as vividly as they do. You can practice this skill though. Sit down and write out your feelings. Yes, I actually just wrote that. If you’re used to writing technical stuff like me this will feel extremely weird and like you’re in kindergarten, but don’t stop practicing.
5.
To be honest, this one is the hardest. I think as an INTJ even if you love your partner more than anything, making them a priority is extremely difficult, at least for me. For example, I can become maniacally obsessed with my work and business success. A few years ago, I was making a living playing online poker professionally, I started building a business and I was graduating from law school. This barely left time for anything else.
For the last few exams in law school, I had to study extraordinarily much, so I did not spend time with my INFP nor did I build my business. After passing the last exam I sit straight down to play poker and code. I was just so angry that I wasted so much time studying and that I was not making any progress in the other two domains that I couldn’t concentrate on anything else. My INFP, who was patiently waiting the whole time I was studying really wanted to spend time with me now that I was ‘free’, but I said no because seriously all I could think about was getting stuff done. Thinking back, I was a real jerk, and I would behave differently now. The lesson here is that no matter how many important endeavors you have, you have to put your INFP first. INFPs are mostly kind, helpful, and supportive, but they definitely have their tolerance levels. If you abuse their support in such a way they are not afraid to make difficult decisions.