Why is it so hard for me to say that I want to quit?

I told my boss , ' I want to study English abroad , so I am thinking about when to quit the job.'
He asked me , ' How long do you want to go?'
I answered , ' One month . '
He suggested , ' If you have paid leave, you can use it and come back to work again if you want.'
Hmm... Of course , I really want to study abroad , but on the other hand , I want to take a rest and use my time for myself without worrying about my job.
Why is it so hard for me to say that I want to quit? I don't want to sound negative, but it's true that I want to study abroad . It's also true that I want to distance myself from work.
He also said, 'After you come back to Japan , if you still think about quitting the job, you can choose that option .'
His words made me decide.