There is nothing problematic about this lack of a duty to love a particular person romantically (Brogaard, 2015). You are not always required to perform a particular action, either. You may have justificatory reasons for going to the gym, meeting a friend for coffee, and calling your mom — all within a short window of time. You cannot do it all. So unless one thing is more important than another, there is no one thing you are required to do (although you may be required to do one of those things).
Likewise, there is nothing that makes me obligated to love just one person romantically, or to love one particular person rather than another. From the point of view of rationality, the only mandate there is that I do not love someone whose features are such that my being in that state subtracts from my well-being.
The view that there can be justifying reasons for love which are based on the physical and psychological attributes of the person has sometimes been criticized on the grounds that we tend to treat our beloveds as irreplaceable (Kolodny, 2003). Most of us are strongly inclined to think that even if a perfect replica could be put in the place of the person we love, this would not quite be the same.
A common reason given for this is that we would not have had the same shared history or past relationship with the replica as we have with the person we love (Kolodny, 2003). On this view — also known as the history view — there can be justifying reasons for love, but these reasons are not based on physical or psychological attributes of the beloved, but rather on facts about the particular history we share with them — for example, the good times we have spent together.
The history view is peculiar for two reasons: First, it seems to confuse past love with memories of the past. But our resistance to someone else taking our current partner’s place is not due to our actual past with the other person. It is due to nostalgia and sentimentality (Grau & Pury, 2014). But the nostalgia and sentimentality that sometimes surround past relationships should not be confused with romantic love (Brogaard, 2015). If you hang onto your mostly fabricated memories of the “good times” and ignore the red flags right in front of you, you risk staying in a toxic relationship much too long.
Second, the history view implies that a preponderance of good times together in the past can be a justifying reason to continue to love the other person, regardless of how he or she treats you now. Current passive-aggressive behavior, gaslighting, or cold indifference would not matter.
Conversely, a preponderance of bad times together in the past can be a reason against continuing to love the other person. Since you fall out of love faster if you cut all contact with the other person, this should motivate you to break off the relationship, and that may be the right thing to do in many ugly cases.