dwell on
• think, speak, or write at length about a particular subject, especially one that is a source of unhappiness, anxiety, or dissatisfaction.
• "I've got better things to do than dwell on the past"
Similar:
linger over,
mull over,
muse on,
brood about,
brood over,
think about,
spend time thinking about,
be preoccupied by,
be obsessed by,
eat one's heart out over,
harp on about,
discuss at length,
expatiate on,
elaborate on,
expound on,
keep talking about,
