I got a bit stuck thinking about this because the 'addicted to him' concept is everywhere, but it never feels like the same thing twice. For me, the obsession trope where the love interest is literally a drug hits hardest—like in those dark romance novels where the heroine describes his touch as a necessary fix, and withdrawal is physical agony. It's not healthy, obviously, but that's the point; the story dives into the ugly, desperate side of attachment that polite society tells us to hide.
Then there's the fated mate or soulbond setup, especially in paranormal. The addiction isn't a choice but a biological or magical compulsion. The characters are drawn together by something bigger than themselves, and fighting it is painful or impossible. It removes the element of 'should I walk away?' and replaces it with 'how do we survive this pull?' which creates a different, often darker, tension. I lean towards stories that use this to explore loss of agency rather than just as a convenient plot device.
Power imbalances really feed the addiction too. Think boss-employee or guardian-ward dynamics where the dependent person's whole world narrows to pleasing the other, making their approval feel like a hit of dopamine. The addiction is to the validation, the security, or even the drama they provide. It's less about cosmic forces and more about how unequal situations can warp desire into dependency. I sometimes find these harder to read because the real-world echoes are louder, but they undeniably get the heart racing in a conflicted way.