a wistful desire to return in thought or in fact to a former time in one's life, to one's home or homeland, or to one's family and friends; a sentimental yearning for the happiness of a former place or time

a nostalgia for his college days.

something that elicits or displays nostalgia.

noun

fond memories , hearts and flowers , homesickness , longing , pining , reminiscence , remorse , schmaltz , sentimentality , tear-jerker , wistfulness , yearning , loneliness