up until the visa expiration date in Dec you can leave and enter Thailand again before that date. Each time you enter you would be given a new 1 year permission to stay date.
If you are leaving and returning after that date you will need a reentry permit to keep your current permission to stay date valid. You can get a single entry permit if you are only leaving once during that time. Otherwise get a multi entry permit. 1,000 baht vs 3,800 baht.