gathering clouds
A sign of impending trouble or danger. (The "clouds" refer to storm clouds.) There have been gathering clouds in the city for months—I'm nervous that a riot will erupt soon.
go gathering orange blossoms
To look for a wife. The phrase refers to the frequent use of orange blossoms as wedding decorations symbolizing the bride's innocence. I'm quite certain that Sir Andrew went to town to go gathering orange blossoms, so we'd best get ready for a wedding!