Why cheat

So I never understood why someone cheats. 
Why do it?
If you want to be with someone else,
just leave the relationship.
Why be in a committed relationship?
If you want to be with someone else, 
then you don't love the one you're with.
So stop leading them on and stop hiding it.
If you feel like you need to hide something, 
then don't do it.
It's that easy.
Why hurt the one you're with?
Why leave them wondering?
If you want to be with more than one person,
Then don't be in a committed relationship.
Just be with whoever you want when you want. 
No need to bring someone in to just hurt them.
I don't understand why. 
I just don't get why anyone would cheat.
Just leave before you do it.
Because if you want someone else, 
you don't truly love them.
Why would you want to hurt the one you say you love.
Just another thing that shows you don't love them.
Because if you did, 
you would not want to hurt them.
Especially like that.
If you want to be with more than one person,
Then don't be in a committed relationship.
Just be with whoever you want when you want. 
No need to bring someone in to just hurt them.
I don't understand why. 
Whyyyy?
Why would you cheat and not just leave?
Why would you want to do it?
I just don't get it.
I don't understand why. 
Why hurt them like that?
Tell me why people cheat and help me understand. 

female, pop, pop rock, punk