This is the 15093rd most frequent Russian word.
покончил
"Покончил" means "ended" or "finished," often implying "put an end to" something.
In this sentence, 'покончил' means he has put an end to something, specifically harmful habits.
Он покончил с вредными привычками и начал новую жизнь.
He has quit his harmful habits and started a new life.
Here, 'покончила' implies severing ties or ending a specific situation, dramatic relationships.
Она покончила с драматическими отношениями и теперь наслаждается покоем.
She has ended dramatic relationships and now enjoys peace.
This usage of 'покончил' expresses the tragic action of ending one's own life (whether completed or attempted).