What does "sweep" mean here? Is it an idiom?
To "sweep in" is an informal expression meaning to move, dash, or run into some place with force. In this song, the singer has used it to express his wishes to see his lover appear again, indicating that he misses her. This is not a common usage for this expression. Usually, "sweep in" is used to indicate forceful movement, which can be literal. Ex: The flood swept in suddenly and pushed all the houses into the river. Ex: The underdog team swept in and won the championship series.