You can always come back within 1 year, as someone said, you'll just pick back up where you left off and whatever time you have remaining in your probationary period will continue.
This job requires a great deal of mental fortitude. The moment you are able to not let the stresses of the field get to your core you will succeed. I would say give it a few more weeks before making a decision. It gets better after the holidays.
Trust me, I am way past well done after being on one of Brooklyn's heaviest routes for the last 4 months and I am finally happy I don't have to go through that again after today. IT gets better with time. Hang in there.