First, this verse I believe speaks to things we do that end up being destructive in our own lives that ultimately lead to sin. Over and over people struggle with things for a bit and feel that God has really done something with their lives. You know how it goes, we struggle with something...get over it...feel the victory...give testimony...and then plop we are right back in it again. The psyche behind this makes no sense and none of us are above it.
Second, this verse can ring true in other vices. Let me speak to that of relationships. As a teenager the "good guys" would always wonder why the "nice girls" would go with the guys that treated them as garbage. They would find a boyfriend and then get treated like trash only to want them back after they break up. This happens as adults as well...friends see friends go through this. Family sees other family members going through this and ask ourselves "WHY ARE YOU DOING THIS!?" Usually the person never notices it but we have to be wondering...don't you see the destructive path this is leading you down?
When the bible says, "those who the Son set free is free indeed" it is not merely talking about our salvation but our bondage to things that make us an unpleasant person. We don't have to be bound to those things that bring sin into our life. We don't have to be bound to things that bring pain and hurt into our lives. We are to experience FREEDOM in our lives, but when we get the hunger to return to our vomit....we don't break free from anything.