"How dreadful!" cried Lord Henry. "I can stand brute force, but brute reason is quite unbearable. There is something unfair about its use. It is hitting below the intellect." ~ Oscar Wilde - The picture of Dorian Gray
It's a very typical reaction for INFPs who feel hurt in some way to withdraw from people. INFPs can be said to have an aloof exterior at times and be hard to get close to in general.
I've gone through instances of losing someone close to me (not to death...rejection) and feeling the need to withdraw socially to deal with my feelings. I needed a protective shell for awhile. We can wound pretty deeply, so it takes us awhile to heal & trust again. Also, just being introverted means you may need to retreat to cope, since interaction sucks your energy.
I also score INTP more than anything, and I am quite sure I am INFP. Many tests seem to ask questions in favor of Fe, so a Fi person may test as a thinker.
I personally don't believe that people change their primary functions, but simply mature and become more balanced....If people change type, it's because they were typed wrong to begin with, IMO
"Charlotte sometimes dreams a wall around herself. But it's always with love - So much love it looks like everything else. Charlotte Sometimes - So far away, glass sealed and pretty." - The Cure