John slipped up last night at the party and had a glass of wine. he called his relapse prevention therapist immediately who told him it was okay, and that he needed to refocus on his sobriety and what led him to take that drink in the first place. john needed this validation and support to avoid

He need the validation and support to avoid abstinence violation effect.
abstinence violation effect makes people who are comitted to avoid a certain substance over a period of time justify their relapse from those absence and ending up over-consuming that substance.
For example, someone who swore to never smoke anymore ending up using it more after 2 month of success because 'they already absence to make up for it anyway'