There is no black or white here. Just a spektrum from idiomatic to literal. Most words can be used in an idiomatic way. Idioms, such as 'Look before you leap.' can be used quite literally. But they may also be interpreted in a way which has nothing to do with the literal meaning. This is nothing special. Words do this too. 'mean' can indicate the idea inherent in a word, but it may also indicate a miserly person. Quite what is meant will not be apparent from the word itself. It takes its meaning from its surroundings, from the speakers intention. Words take on other meanings, so do phrases.
The best use of 'falling out' I know is from Bob Dylan: We had a falling out, as lovers often do, but to think of how she left that night, it still brings me a chill.