The letter in the New Testament which we call "First John" says that "perfect love casts out fear." This is true but so is the opposite: "Perfect fear casts out love."
This can happen in many ways. A man or woman can be so fearful of expressing an interest in someone else that a romantic relationship never gets a chance. Someone who has hurt somebody else can be too fearful to apologize. A young person can choose a profession which is not his or her first love in out of a fear of parental disapproval. Fear that others might leave can prevent someone from insisting that they treat him or her respectfully. Fear of the worst that could happen can prevent someone from judiciously letting a wrongdoer experience some of the negative consequences of bad choices even though this is the most loving thing to do. Fear can make it impossible for someone to leave an irredeemably hurtful relationship. We could go on and on.
So, yes, perfect love casts out fear and perfect fear casts out love. Every increment of feeling more love reduces fear somewhat. Every bit of feeling less fear increases love correspondingly. Either of these by itself doesn't work. It has to be a two-way street on which the traffic slowly moves in both directions.
Yet I John is not talking about fear in general. It is addressing the specific experience of fearing God's punishment. It says that those who know firsthand this kind of fear have "not reached perfection in love." In other words, they have yet to make wholly their own the good news that God loves them. This is why it immediately says that "we love because he first loved us."
Whether we begin with increasing love or decreasing fear has to be determined on a case-by-case basis. The important thing is to keep them interacting.