Example 1
I graduated high school 6 years ago. I have heard that my high school teacher is shooting videos and no longer teaches.
Example 2
I graduated high school 6 years ago. I have heard that my former high school teacher is shooting videos and no longer teaches.
Is "former" necessary in Example 2?
Background info: I broke up with my girlfriend years ago. And I don't have a girlfriend now.
Example 3
I ran into my girlfriend.
Example 4
I ran into my old girlfriend.
Is "old" necessary in Example 4?
I have problems telling when I should use "ex-," "old," or "former" in a case like this.