I find it interesting, because in general, infjs are actually fairly opinionated people that are not doormats. However, they do rely on others more than most types to mirror back to them what they are like, whether their internal response is appropriate to the situation, and need a sounding board to process their thoughts. They are usually choosy about who they allow to perform this function, but once they've let them in, the person holds most of the keys and can mess with their sense of reality. I think we rely heavily on being sure of our perceptions and having enough info to work with to navigate well.
Often, people that are attracted to warmth and listening because they haven't had that can have some emotional baggage of their own, but cover it up with a sort of false confidence and do a lot of push and pull emotionally. Initially, they may even be caught up in the euphoria of feeling understood and appear very open. However, they cannot sustain it long term. They may react to feelings of fear or vulnerability by being controlling or withhold information and find it hard to be honest, at other times letting you in enough to see that there is a different side to them as well with a lot of the attractive quality you originally saw.
I think infjs are also attracted to decisive people, they tend to allow others to take the lead and are not always proactive about seeking out people, but let people find them. So all of that can contribute to some of the dynamic.
I am normally a pretty happy, confident, self sufficient person, but have had a couple of relationships where suddenly the person acted like I was hovery and smothering. The fact was, they would not resolve conflict and also needed to be in charge to feel secure and were not open with relevant info (maybe they didn't even know how to talk about their inner world or were consciously aware of what was going on) and I unconsciously reacted by trying to ensure things were okay because their assurances that things were fine did not match the behaviour.
Anyway, I recognize now I that I was a part of allowing the dynamic to develop, but I also let it continue because it was bewildering to have my perceptions be so different from those of someone whom I lived and whose opinions on I valued. Once I understood what was going on, it was less hard to take action, but I usually needed a second person to voice the same perceptions for me to trust my own.