How do I execute the else only once, ie once the LED2 is LOW, no further digitalWrite; and same for LED2 set to HIGH.
Do you really care if the digitalWrite()s happen over and over ? The Arduino certainly won't care
If you do, then introduce a boolean variable with a suitable name, perhaps ledHasBeenWrittenTo and set it to true when you write to the LED and make the writing to the LED dependant on the variable being false. Change the variable to false when you change the state of the LED