Why do some people have a harder time letting go of relationships?

They fear they may never meet another person like that person.

Which is a legit possibility I’ve found.

Because they don’t realize that life can be better alone, rather than staying with, or pining for, a person or a relationship that wasn’t beneficial for them.

There is no right answer to this question. It is like asking why your car won’t start with no further details.

And really, just get a cat and a hitachi.

Because they still have hope that something will work out?

In order to insure survival, instinct derived predilections guide an infant to bond with nurturing adults. This mechanism is the basis for all relationships. Fear is generated when a relationship appears threatened, and we unconsciously seek ways to secure it. As with any significant loss, grief in all of its stages is experienced when a relationship ends.

Because they’re afraid to be alone?

@BellaB I believe that until one has acquired confidence in their ability survive without total dependence on other individuals, instinct will generate a state of fear that can overwhelm rationality. However, fear is not the only emotion involved with an attachment to another. Relationships provide the opportunities for the satisfaction of many psychological and physiological needs, such as companionship and asexual intimacy. The more friendships a person has, the easier it will be to work through the stages of grief.