Over the past two years, many countries have implemented various social distancing policies to contain the spread of COVID-19. As the pandemic continues for a long time, intervention fatigue is starting to play a major role with outcomes that differ from the expectations of social distancing policies. Thus, we consider changes in policy adherence due to intervention fatigue in evaluating the effectiveness of social distancing policies. Through an agent-based simulation, we investigate the impact of policy adherence in various social distancing scenarios that differ in how the contact networks between people are restricted. We find that a trade-off between policy strength and policy adherence arises when considering state-dependent policy adherence. We further investigate the sensitivity of the number of infected to the slope of the decrease in policy adherence according to the strength of the policy. This suggests that it is necessary to design social distancing policies in consideration of changes in policy adherence.