I almost always know what I am thinking and feeling, I just sometimes have trouble conveying it in a satisfying way, especially if I am concerned about the other person’s possible reaction or being misunderstood.
I agree; I definitely know my own mind & heart. I'm even decent at picking up on other people's feelings...usually. Attraction can kind of throw a wrench into this. I worry wishful thinking will get in the way. I honestly worry I will allow fantasy to tamper with my interpretation of reality. So I tend to question signals from people I'm attracted to, unless they are very clear.
And yes, the OP seems to have made his intentions very clear, and so I think it boils down to disinterest from the INFP, or maybe not being emotionally ready for a relationship & recoiling when faced with the possibility of one (despite genuine attraction). In any case, I think the typical INFP who was interested would've given a much clearer response to a direct invitation. Whatever excessive humility, oblivousness, doubts, awkwardness, etc, may come into play, at a certain point you either really like someone or you don't & you act accordingly, especially when they've made their interest known (this is why I still think some of these INTJs in my past were not so smitten as they later claimed; why the vagueness & half-hearted attempts to get together then?).
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And the ENFP vs INFP thing going on here is sort of bizarre. I don't see any reason to pit the types against each other. While there can be a similarity in thinking (most evident online to me, where I'm surprised at how much similarity there is), they tend to have VERY different demeanors. The OP stated he was NOT interested in the ENFP romantically, so it's not a matter of which is better for him. What type is best for your type in theory means little when you're attracted to a living, breathing person of another type who just might like you too. The OP is unlikely to swicth his interest based on theory. This a matter of whether the INFP likes him or not, or if he can turn a mild interest into more. The ENFP in question went out of the picture pages ago...