In just four short lines, the speaker looks back at a moment of loss and admits to a tangle of reactions. They cried and screamed for someone, which suggests a love or attachment that was intense and maybe painful. Then, when that person finally walked away, the speaker laughed, and kept laughing.
The laughter is the strange part. It could be relief at being free, or bitter mockery of themselves, or the kind of hysterical reaction that comes when grief gets too big to hold. The title, "Foolish," points toward that last idea: the speaker seems to judge their own behavior, perhaps feeling silly for all the tears and shouting that came before.
The mood is raw and unsettled. The lines are plain and the repetition of "I" and "laughed and laughed" makes the poem feel breathless, almost out of control. We're left unsure whether the speaker has healed or is just covering the hurt.