I have some experience here........
How do you experience this type? I have seen at least 3 long term romantic relationships between SEI and LSE, and have noticed many life long friendships of these two types.
In generally they seem quite cute, feminine, caring, and in need of logical and productive assistance. I have said numerous times, "man, she would be a great person to be in a relationship with", although prior to socionics. There is a great deal of superficial attraction, and appearance of chemistry.
Friendships seem very close and have little trouble remaining this way, although at times the SEI will make negative comments about LSE behavior behind their back. I have never seen LSE talk about SEI in this way.
It is easy to be close, because I generally do understand ISFps pretty well. One of my closest relationships is with an SEI. We both ponder intuition and religion and other things. They are flexible and generally don't seem to cause trouble, and protect my week emotional and relational areas fairly well. They are not often over the top with Fe, or they at least are nicely aware of my own mood well enough to make sure things don't get out of control in my presence.
Of the three romantic relationships it was the SEIs who eventually broke it off, and the LSEs have taken this very hard. It seems like they just don't get why it didn't work, and they hold on to this for a long time.
This is a very good thing to observe, it will help you understand socionics and people better.
Why it sputtered out is because (I have seen this with myself and with an ESE), bluntly, the LSE and ESE are rational. They are predisposed to consistent relations. This eventually wears on the SEI - and it is often nothing really "rational", there are no "rational" reasons behind why they get bored, they just do. It is because they need more change and just a different kind of relationship. Why the ESXj takes it so hard is because they want and long for an IJ type. The ESXjs feel like nothing is wrong because they just don't realize that anything is wrong. Simply by being who they are, this slowly turns off the SEI, because the SEI needs Ne. Someone who is so consistent, as ESXjs eventually move towards, bothers the SEI, because the SEI feels like they are getting stagnated and losing "who they are", so they need to find themselves somewhere else.
From the end of a marriage that I witnessed between SEI and ESE, the ESE took it horribly, because the SEI became sexually dissatisfied and cheated. The SEI was not happy with it, but, it just got so bored with how things were going. Having an EJ caregiver and an IP caregiver is strange, because both want to take care of the other, and there is no one who genuinely needs it or appreciates it, like an infantile does. So in this case, the ESE thought it really was doing its job - because things were consistent and steady, and that is good. That is what its dual, an IJ, is looking for. But the SEI is looking for an EP static, not an IJ static.
There can often be attraction based on morals or beliefs or physical appearance, but in the end there is much more than that, there has to be raw compatibility and life alignment. In the marriage I described, the ESE was giving adequate space to the SEI, and the ESE thought was doing things right, because, for an LII, that would be what it wants. However, the LII would be much more receptive to care giving ways.... towards the end of the marriage, the SEI made remarks like "(The ESE) just got colder over the years...", and what that really had to do with was the ESE feeling like the SEI did not need it's "care", so it stopped giving it. Later, the ESE ran into an LII, and seeing someone who so greatly needed their natural ways, it was a great match.
In much the same way, the SEI started looking for someone to take care of, because the ESE, who was very settled, just didn't need them that much.
In this way, I can see an SEI being attracted to LSE's nobler qualities or stability, but ultimately being turned off in the long run because the LSE is not someone who needs (to be "taken care of in a caregiver way") very much, if at all.
(note: I see this happening with a double ESE couple... they are very nice, and seem like a pleasant couple, and may stick together ethically, but it seems to foreshadow a lack of success, unless each one keeps rotating into and out of playing the role of their dual)
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Personally, there is usually a general attraction to ISFps, because they take care of themselves pretty well, and like I said, they can be really feminine, which is attractive to me. So there is a lot of initial "green lights". But over time, their alpha-ness and focus more on immediate happiness and need of Ne/weak Ni/ lack of direction seems to get odd. I see them as "stagnating" or needing help from me that I don't really know how to give. We are both looking for the same thing and neither one of us really has it.
ISFps generally make great discussion partners because we both approach relationships in a similar caregiver way, so to say, and they make good and easy conversation about anything. You can always just talk with them. But ultimately they don't have the substance I want, and they don't quite have the same outlook on life as, say, EIIs.
ISFps seem to "appreciate" my
advice, but they don't really ever use it, and don't really seem to be too concerned with actually being efficient about getting somewhere. I feel like supervising them is like..... being a father, and them being children, and I'm saying "do something useful with your life, pick a job that is important and matters", but they just don't really get it, and want to be artists or musicians or just some other..... 'go-nowhere' sort of job. They seem pretty bad with money in general.
My ultimate conclusion about the type is that they are great friends for me. But they lack the seriousness, rationality, stableness, and need of me caring for them that EIIs automatically have, so in that way they seem unfulfilling as real, long term partners. They just seem like children, basically. I feel responsible to take care of children somewhat, but I know I need a real adult, a woman, to be in a relationship with. (Consider this from an alpha vs delta perspective, not anything personal against the type).