Nostalgia

A sentimental longing or wistful affection for the past that is a predominantly positive and social emotion. Nostalgic experiences typically feature the self as a protagonist in interactions with close others or in momentous events.

Reference:
Zhou, X., Wildschut, T., Sedikides, C., Chen, X., & Vingerhoets, A. J. (2012). Heartwarming memories: Nostalgia maintains physiological comfort. Emotion, 12(4), 678-684. doi: 10.1037/a0027236

Wildschut, T., Sedikides, C., Arndt, J., & Routledge, C. (2006). Nostalgia: content, triggers, functions. Journal of Personality and Social Psychology, 91(5), 975-993. doi: 10.1037/0022-3514.91.5.975