The bolded part I understand very well. My relationship has been a huge learning process for me and one of the most surprising things is that what seems natural and normal to me is completely foreign to him and vice versa. I was totally caught by surprise when my INFP said to me, "I appreciate your concern, but you don't have to fix everything. It's all right to be sad."
I realize there is a huge gap in our understanding. Like I've said somewhere before, I feel that INFPs are like a mirror image of myself. I can recognize myself in you, and we can see that we are so similar, but my right is your left, my left is your right. This makes the dance much harder than it looks in the first place.
So as not to stray too far from the topic, I will stick to what Fe (at least for INFJs) does and why Fe relationships end. The basic thing is: Fe needs that constant exchanging of emotional energy, or it shrivels and dies.
Because of its merging nature, Fe needs constant communication. Like a river, it comes from somewhere, and it goes somewhere. Everyone's feelings are connected. Also like a river, when it goes to dry land, it tries to work its way through, to moisten it. Its perfect vision is to bring life to it, and little by little the grass grows, and a forest grows, and the dry land is not dry anymore. Finally, with a forest there, it rains. The rain fills the river and the river can continue to flow more to the land. On the other hand, if the river perceives that there is no hope for the land, meaning that the grass won't grow, and whatever effort it puts in seem to go through the cracks in the ground and disappears, it gets disheartened. If this persists for a long time it dries up for good.
Fi is like a deep well. We truly admire the fact that your feelings are pure and true and, at least compared to ours, unaffected by the environment. We truly admire that Fi love can hang on for years and years and years even when there is no hope. There doesn't have to be rainfall to replenish it. However, coming from our perspective, we don't know what is there in your deep well. In the end, we don't even know if there is water in there. This, together with the changing nature of Fi -- you want one thing one moment and another thing the next -- scares us. We have no idea what you are thinking about, what you want, what you are really like inside. Sometimes we feel like we don't really know you. Who is it that comes out once in a while with all those wonderful qualities, deep, caring, sensitive? Is it the same person as the one who shuts us out without warning and leaves us in the dark? When we perceive no consistency, we cannot be sure that what we have is really good. We can't even be sure about what we have at all. This scares us to the core and as time goes on we are convinced that it will not work.
Going back to the light analogy, if we cannot keep the 'us beam' blue, or whatever color we both have decided is good for us (which, with INFPs, most of the time we have not even decided on the color we want in the first place -- and most likely we will decide for you, because we cannot NOT focus on a color, and which you might not like), we get confused, we panic, we feel like we are doing something wrong. We feel like a failure and that it's our fault that we cannot make you happy. Then we despair. Over all this time, with all the effort, all the caring, we feel unappreciated, unloved.
This is why good communication is the key. Give us something. We need a sense of direction. Sometimes it helps to be able to tell us objectively what it is all about. Let us know there is water in the well even when we cannot see it, and that it will not dry overnight. A river flows constantly. The only time it doesn't is when it gives up. For us, when we don't feel the water, we think you have given up, and we try to figure out what we have done wrong to make you withdraw your love so easily.
The thing is, we need the very thing that might feel intrusive to you. We are reassured when you let us in on your problems, when you tell us what you want from us. Explaining to us how you don't need for something to be a certain way helps a lot more than you think. When you feel we are intruding, tell us.
The difference between J and P is that being a J, we want at least one color on the wall that we can work towards. You, on the other hand, don't mind if it keeps changing. We feel that the changing colors are too confusing, because we orient ourselves to the color we see on the wall. Too much change and we feel like we are constantly being tossed around in a whirlwind and we feel very uneasy and restless. For you, one color seems too constricting. You feel trapped, caged. The whole thing feels forced. At the very core, I think the only way for an Fe/Fi relationship to work out is to be able to find that balance, that middle-ground between stillness and movement. Find a range of shades you can both live with and within that range let the colors shift.
So, you need a whole lot of adjustments on both sides. Communication is everything. So far, in this relationship, sometimes the only way I can get through to him is to drop all my defenses and lay bare my soul for him to see. It takes a lot of courage, as I become completely vulnerable. But that's my leap of faith -- faith that he will catch me and not let me fall.