Make a new plan' is just making a plan, it's not a way to leave.

Disagree! Telling someone to "making a new plan" is quite clearly a "sod off" statement. Some people try to soften the blow with more prosaic language.

I well remember a GF saying to me "that woman fancied you" - how oblique do you need it?

Another (soon to be) ex-SO said one day "I have rented a cottage" - they need a way to broach the subject - which is the premise of the song IMNSHO.

A lass I lived with for 10 years spent 5 years being contentious, hoping I would get fed up. When I did she changed her mind!

50 is such a small number but it is alliterative, though 55 would have been moreso. All of which just proves that Paul Simon is a master wordsmith. Gives us 5 examples and we add the rest! We nod in agreement.