Lisa believes that drinking alcohol is wrong. however, her boyfriend mike likes to drink beer after work. instead of breaking up with mike, she decides that drinking alcohol is not so bad after all. lisas attitude most likely changed because of

Cognitive dissonance - Lisa was feeling discomfort at the fact that her boyfriend was doing something she disagrees with. In order to relieve the discomfort, she decided to change one of the clashing things - she chose to conform to her boyfriend's ideas and ditch her own. She could have also chosen to justify her actions.