There’s actually some research that suggests when we become "addicted" to a song, especially a sad one, it’s because of how our brains process emotions and seek patterns. When we listen to a song repeatedly, our brain can release dopamine, a "feel-good" neurotransmitter. Even though the song might be sad, it can trigger a sense of comfort or familiarity, which is why we crave listening to it again.
In terms of emotional processing, listening to a sad song can help us process feelings we may not be consciously addressing. Our brain may use the song as a way to work through unresolved emotions, especially if we associate the song with a meaningful moment or experience. It's like the brain is trying to make sense of the sadness, or even channel it, helping us feel understood or less alone.