I enjoy cannabis nearly every day and night of my life. I also clean up after what amounts to a twelve-hour-long homosexual orgy pretty much every night. Jizz, condoms, urine, blood, cigarette butts so covered in cum that they will not come off the floor even using a paint scraper, skeet skeet skeet visibly on the walls and all. Nobody expects very much out of a guy that mops male ejaculate for a living, so I can stay pretty fucked up constantly without incident.
You are training to be a dentist, yes? If you are using painkillers, benzos, or hard drugs: GO TO REHAB IMMEDIATELY. Marijuana is not an answer for depression, it is fun though.
In your case, I would say the cure would be to find a new lover. I had an old man tell me the best cure for depression was a fat cock. He seemed wise enough.