The speaker is hurt and confused because his partner has ended their relationship after he believed they were committed to each other. At first, he struggles to accept the breakup and says he still cannot do without her. His feelings then shift toward resentment: he believes she will eventually experience the same pain she caused him.
โWhat goes around comes aroundโ means that people may eventually face the consequences of their actions. The image of someone having him โin the palm of your handโ suggests that she had great power over his feelings. Later, the repeated calls that reach a โbusy toneโ show the new partnerโs absence and leave her lonely, echoing the speakerโs earlier hurt.
The ending presents her unhappiness as a kind of payback, but the speakerโs satisfaction is mixed with bitterness. He may feel that events are fair because she is now being treated as she treated him, yet he also sounds wounded and unforgiving. The lyrics portray this as a return of consequences, though they do not prove that every painful event is deserved or that the speaker has truly moved on.