Where can I find this theme?

Can someone name a book, movie, or song that deals with this theme:

Two people, Pat and Kelly (for example) are in a toxic relationship. Pat reaps benefits from the relationship without bearing the cost, at least not as much as Kelly. Kelly endures most of the toxicity but is hopelessly devoted to Pat. Kelly will always pour energy into the relationship despite the damage. Pat finally becomes aware of the situation and selflessly lets Kelly go.

Example instances of this theme could be:

  • Kelly works for Pat as an apprentice. Kelly’s skill develops to the point where it’s time to strike out alone. Pat needs Kelly’s continued help and intentionally or inadvertently sabotages Kelly’s attempts to break away. Kelly feels indebted to Pat and continues to work. Finally Pat realizes the situation and helps Kelly branch out.

  • Kelly is married to Darcy and having an affair with Pat. Pat lives a happy go-luckly lifestyle and all is well until Darcy finds out. Kelly is now facing the divorce, custody, etc. and wants to end it with Pat. Pat, not fully understanding Kelly’s turmoil, continues romantic overtures that Kelly can’t resist. Again, Pat finally realizes the situation and lets Kelly go.

  • Pat is Kelly’s parent

  • Pat and Kelly are lovers, but Pat’s wreckless lifestlye is incompatible with Kelly’s health, or values, or…

  • etc.