Effacer means "to erase" or "to wipe out". It's a central theme in the song, as the artist grapples with the inability to erase memories of a past relationship.
The lyrics state, "Je ne peux pas effacer les souvenirs du passé" (I cannot erase the memories of the past), highlighting the pain and permanence of these recollections. This word is emotionally charged and directly relates to the song's title and core message.
"Effacé" is KOFS looking back at a relationship he broke and can't quite let go of. He opens by admitting he hurt her before running off, and spends the song replaying the good years: trips together, promises made in front of the mayor, quiet nights by the sea.
The chorus is the heart of it - he can't erase the memories of the past, even though he knows moving on would be easier. His pride keeps him from telling her not to leave, but he still hides the truth from his own mother, who had approved of this one girlfriend more than any other.
By the end he says he's gotten used to being without her, but the song's own repetition says otherwise - he's still stuck replaying what they had.