I was reading a book last not on compulsive behavior around food by Geneen Roth when I came across this line:
Compulsion is despair on the emotional level. The substances, people or activities that we become compulsive about are those that we believe capable of taking our despair away.
While compulsive behavior and addiction are impossible to define in a single quote, there's a lesson here for our real lives as well as the internal lives and motivations of our characters. Every person is in some way seeking to remove or prevent or avoid despair. Some people do this in healthy way, such as connecting with people and allowing themselves to be loved. This does not mean that people who prefer to spend a lot of time on their own are filled with despair, but it does mean they have at a few relationships that provide what they need.
Then there are those for whom despair means sliding into addictive behaviors and believing that ultimately there is a person or substance that will remove their despair. Someone drinks because it fills the hole within their soul. Someone eats compulsively because when eating they are able to keep despair at bay. Someone exercises to a compulsive degree because the endorphins released enable them to escape despair.
However, these are temporary salves. For each, when the effect wears off, they are left in the same emotional state, vulnerable and in need, that they were in when they picked up the drink, doughnut or dumbbell. They haven't resolved their internal and external conflicts, their flaws or idiosyncrasies in order to ameliorate their despair.
There is one pure and simple way to begin the heeling and that's through allowing love to enable them. This is not dependent upon another person or relationship, it simply means allow yourself to love. The key here is the point of view. It is not dependent on being loved, but on allowing yourself to love. Open your heart.
Easier said than done, of course.
For a writer, this insight leads to a number of thoughts, ideas and implications. Even if your genre is fantasy, your protagonist is seeking something and more often than not it is to keep despair (the bad thing) from happening. How does the drive to remove despair from your character's life compel certain behaviors? What compulsions would that person have, even subtle ones, that they use as tools to keep despair away?