The speaker looks back on a close friendship that faded as both people changed. They once laughed and played together every day, but life pulled them apart. When the other person drifted away, the speaker let them go with a smile and said, "Don't worry I'm not mad." The poem suggests that this calm surface hid a lot of hurt.
Now the speaker is stuck. The friend seems happy, while the speaker is left with regret, sorrow, and a mind that keeps returning to them. The question "How did you abandoned all this so Easily?" shows the sting of feeling forgotten, and "I will never know" admits there may be no answer.
The mood is wistful, anxious, and a little lonely. The repeated line "As we changed" works like a heavy refrain, and the ending turns fear on the other person: someone once so familiar now feels like a stranger.