I am sorry to hear you are hitting a tough patch especially as things have been going so well recently for you. Have you considered private tutoring as an option. This may offer some financial security and you would not have to deal with so many teens at once. They do seem to have a pack instinct and once they feel weakness then it is a downward spiral. If you are already feeling bad they can make a bad situation worse.
Also talk to your doctor as they may be able to change medication to help stabalise your emotions and help you feel in control. Depression comes in cycles you know from experience things will get better. You also know that you may have episodes in the future and you are right that planning for those whilst you are coping better is so important. If you have a plan you have a degree of control even during the bad times.