What to do and how to cope when I accidentally forget to take my antidepressant medication?

Long half life meds. Try reminders: pill box, alarm clock. Sync medication timing with your daily routine activities, such as breakfast or dinner time. Consider switching to meds with long half life. Wish you good luck.
Usually it's ok. If you forget 1 dose and remember it within a few hours, take it. Otherwise skip it, and don't double-up the next dose or take extra. Antidepressants work over weeks, so 1 missed dose won't matter. If you forget 2 or 3 days in a row you may have withdrawal symptoms, uncomfortable but not dangerous. Get back on your usual dosage schedule asap.
Missed dosage. Best thing to do is to make up your missed dosage and report to your doctor the results of this.