Do you know how to heal your heart?
You find a new love. It's not about forgetting, it's impossible to forget someone who affected your life in a great extent. The past holds as little reality as dreams do. It becomes like a figure of imagination. The image washes off blurry, a distant, and an unreachable reality of the past.
If the new love is true, and everything about it is real; where nothing seems like a fantasy, then the old love will naturally wash away. Just because the memories or the thought of the one you use to love doesn't sting your heart that awfully, doesn't completely mean you have forgotten about the past. It's because you've found a happiness greater than before. With that happiness supporting you and guiding you through, your able to let go.