For me "I Lived" was a love letter ", but somewhat of a different kind. It's as though this person in the song is wishing and hoping that all of what life has to offer, emotional pain (broken bones), challenges (water rising/building a wall), their success and failures, to always give it all you can and make every day count. This person is saying these things to those who were once in his life and that he acknowledges and owns up for his mistakes while he lived, but although he's no longer alive to be present to witness and experience all their joys and all their pain he's sharing a life lesson by passing along a message. That each person who touched his life not to feel saddened over the loss but to celebrate the life their given.