'To fall out with someone' = To no longer be friends with/to argue with someone. 'John used to be my best friend but we fell out.'
'To fall out of something', 'My wallet fell out of my pocket'.
'To fall down', 'I tripped over a loose paving stone and fell down.'
'To fall off' To reduce, 'Sales fell off last month.'
'To fall off', I was so drunk I fell off of my chair.' 'The cup fell off the table and broke on the floor.'