The Chainsmokers - P.S. I Hope You're Happy Lyrics Meaning

This is a song about a while after a breakup, checking in to see how your ex is doing, and realizing all your faults that led to the downfall of the relationship, and going through all the thoughts of regret that lead you to believe you definitely still have feelings for them, but are satisfied with the end result and are ok with her moving on to a new guy.