Serotonin promotes learned helplessness, rigidity, depression, aggression, and dependency. The rigidity interferes with resiliency and the independent mindset necessary to handle rejection in a healthy manner. Unrequited "love" can be seen as a fixation that puts a condition on your own happiness and ability to feel love in that you are helpless and dependent on the acceptance of others. In fact, unrequited love isn't love at all. It's more of a waiting and a longing to receive love partly created by a delusion that love is inaccessible except for certain outward circumstances. When we place a condition on when we feel loved, we leave our souls subject to the mercy of an uncaring, indifferent universe.
This way of thinking will seem foreign to those who define love as an action done to others, and that to feel love, love must be given. But love is a feeling you have on the inside, so love is truly an inward state of mind. (Only that when you feel love, it tends to change your behavior towards others.) Just as some cars take more effort to get started—maybe requiring a jumpstart, changing out a sparkplug, refueling the tank, etc—some people require more conditions—even if unnecessary—to start feeling a certain way. Love was always there—never taken or existing without you.
The point isn't necessarily to coerce you into becoming a being of pure love but to remind that you aren't trapped and helpless. Your happiness is dependent on you—not others—and what you summon forth creates the world you live in—whether that world is heaven, hell, or anywhere in between. I think you will find more people attracted to the ones shining the light of heavenly realms from their eyes than the fires of the hellish realms.
>In CIA interrogation manuals learned helplessness is characterized as "apathy" which may result from prolonged use of coercive techniques which result in a "debility-dependency-dread" state in the subject,
— https://en.wikipedia.org/wiki/Learned_helplessness
(You don't have to undergo literal interrogations/torture for learned helplessness to occur.)