The rapid advancements in Artificial Intelligence (AI) are reshaping language education, raising concerns about the professional future of English as a Foreign Language (EFL) teachers. While existing literature often highlights the effectiveness of AI tools, it tends to overlook their impact on teachers' relevant expertise development and emotional experiences. This longitudinal study addresses this gap by exploring EFL teachers' emotional landscapes and adaptive expertise development through the lens of positive psychology. Employing thematic analysis, the study draws on data from three rounds of semi-structured interviews with ten EFL teachers, complemented by students' post-class reflections and classroom observations. The findings highlight the pivotal role of positive emotions in EFL teachers' professional development, revealing a dynamic, non-linear interaction between positive and negative emotions as teachers navigate AI-integrated language education. This emotional interplay is significantly influenced by teachers' social connections and professional backgrounds. The study underscores the need for institutional support systems that promote positive emotions and enhance teachers' digital literacy. By deepening our understanding of EFL teachers’ emotional experiences and professional growth within the AI-integrated educational context, this study offers valuable insights for designing targeted interventions and curriculum reforms that foster effective collaboration between human and AI intelligence in global education.