I have always pegged the INFP personality type with the Insecure-Avoidant attachment style (I learned about attachment theory in A Level Psychology). In a nutshell, an attachment style is the style in which one forms relationships with others, and those with the Insecure-Avoidant attachment style tend to struggle with emotional intimacy due to how they were raised by their caregivers (usually parents). I think, as well as INFPs; ISFPs, ISTJs and INTJs tend to have this attachment pattern (introverts with Fi).
I would strongly recommend watching this video, as I found it fascinating, and could relate to all of it. I wonder how many other INFPs can relate to this style of attachment. I would love to hear other INFPs' thoughts on this subject.