Pink Floyd - The Final Cut Lyrics Meaning

It's about PTSD, or at least that's what we would call it now.

The first two verses are about the mental state of the survivor, as seen through his eyes. He's is not 'flying', he is hiding behind The Wall of his own paranoia.

And yet he can still remember when he was young and had dreams.

The reference to Dark Side is obvious (DSOTM) but it here has a double meaning, and the guy is wondering what his wife or partner would do if he was completely honest with her. Would she freak or flee or cash in?

He chooses suicide but back out at the last moment, saved by the bell of the phone= ringing.