You change for two reasons. Either you learn enough that you want to, or you've been hurt enough that you have to. (I'm hurt enough to need to change. But I must learn enough of myself to decide what and how to change.
Life is about balance. Be kind, but don't let people abuse you. Trust, but don't be deceived. Be content, but never stop improving yourself. The best collection of quotes and sayings for every situation in life.
Letting go isn't blocking memories or thinking sad thoughts and doesn't leave emptiness, hurt or sadness. Letting go isn't about loss and it's not defeat. To let go is to cherish memories, and overcome and move on.