a memory, recollection, reminiscence / a keepsake, memento

更ける, 深ける: to get late, to get deep (for night, season, etc.) / 老ける, 化ける: to age; to become old

sentimentality

immersed / soak / dip / steep / moisten / wet / dunk

to be soaked in; to be flooded; to be submerged / to be immersed in (joy, memories, alcohol, etc.); to give oneself over to; to bask in

ancient times, a very long time ago

the past, old times / ancient

he / distal demonstrative, something far off removed from both speaker and listener: that / boyfriend

once (in the indeterminate past)

olden days; former