Is it permissible for a young man in his twenties, residing in a European country, who suffers from anxiety, depression, and stomach pains, and whose psychological state worsens and life comes to a halt during the 18-hour daily fasting period, to break his fast, especially since he has stopped taking medications that conflict with fasting?

The illness that permits breaking the fast is one that increases the sickness or delays recovery. This is determined either by the trustworthy physician's advice or by experience. If it is not so, then fasting is obligatory. Obedience to Allah is one of the causes of treating depression, so you should frequently remember Him, supplicate Him, resort to Him, and rely upon Him, along with taking medications and following up with doctors.