Needle and Thread Psapp

You're on your last legs
Don't need me
There is no backup
No cut key
There is no master
If I lose you
There is no needle & thread
That will mend you (mend you, mend you, mend you)

Don't you break
I will not let you
I'll make sure
They will not get you
Don't you break
I will not let you (I will not let you)
I'll make sure
They will not get you

There is no good pen
To write you down
There is no spare part
No common ground
I can't divide you
Cannot make you stay
There is no simple sum
No other way