Hey, I wanted to suggest a shortened version of your post - I just cut out the superfluous information, try posting this in /r/relationships:
I [21/m] have been dating my girlfriend [19/f] for about 2 years now. This is my first relationship.
I feel that overall we have a great relationship, but there is an issue we cannot agree on and it is causing problems.
She is happy to smoke weed with me occasionally, and drink with me occasionally, but WHEN I smoke or drink without her she completely changes for the next few days and it is hell for the both of us.
For example, if I am back home with my parents for the holidays (we are both at university so we are flatting separately but basically live together anyway as we stay at each others flats all the time) and she is either back at home with her family or staying at her flat, and I smoke weed with some friends or alone just ONCE, she will treat me horribly and make my life a living hell for the first two or three days when we get back together after the holidays (e.g condescending, calls me a druggie, tells me how much I hurt her, and basically she cries excessively and is in misery most hours of those days). She will intentionally try to hurt me emotionally, because I have hurt her by smoking without her and she "has to get back at me to make things even". One of the ways she tries to get back at me is she threatens to get drunk or smoke without me, so I "know how it feels" but I tell her that if she does it responsibly I don't really mind.
During one of the holidays (3 week holiday) I had an injury and the pain was preventing me from sleeping. I decided to use marijuana to help with the pain, and after smoking the pain was gone and I slept like a baby. When she found out, she was a miserable mess for about 2 days and tried to hurt me back. This cycle has repeated any time I have used marijana to treat my pain or sleeplessness.
She has the same attitude about alcohol. She is happy to drink with me but if I drink on my own or with friends she gets upset. She tends to look down on people who smoke or drink (she's very judgmental about it), she thinks it's disgusting, yet she will indulge herself with me sometimes.
When we talk about it she acknowledges that her behavior is completely irrational and controlling, and she tells me that she cannot control the way she behaves and she has no idea why she does this. In the end she just ends up telling me that this is what I have to put up with if I want to be with her. Just today she tried to break up with me because she said I deserve someone better, she said that she will just end up holding me back from experiences and controlling me for the rest of my life and I don't deserve that.
I will admit that I have previously used marijuana and alcohol to excess. After we first got together I told her details about my past use, and I was completely open with her. She wasn't too happy to hear about it but is very happy that I cut back my alcohol/weed usage significantly. These days, most of the time we've smoked it was her idea. She tells she enjoys doing it with me and other times she tells me it's so I don't end up doing it on my own.
When I drink or smoke (with or without her) I am careful not to over-do it and just have a fun, peaceful experience and remain in control. I have never done anything I regret under the influence, and I do my best to be responsible.
She does sometimes tell me that I have an addictive personality because of my past and she's afraid i'll become a fully blown stoner or alcoholic. It seems like she thinks that if i indulge without her then there's a risk i'll become addicted.
In the past I have experienced moderate social anxiety and depression. I admit that at that time in my life, my higher consumption was somewhat a coping mechanism. However, I overcame these issues by exercising more, eating more healthy, and most importantly meditation. I got into a routine of practicing meditation and eventually I was doing it 1 to 2 hours per day, which I still do to this very day. This resulted in me becoming almost scarily euphoric whenever I wanted to...I just meditate. I NEVER EVER feel stress in my life, barely ever feel anger or frustration...it takes a hell of a lot to get me angry or upset and when I do I meditate and within 5 minutes I am feeling happy, peacefull and motivated to do chores, study, exercise, or anything productive and healthy.
She on the other-hand gets stressed almost daily because of the mountain of study we have to do for our engineering course at university (getting good grades is very important to her, she does better than me but I'm still doing great and am not very far behind her). She also gets stressed, angry and upset over many other small things. When I suggest meditation and exercise she almost flips out at me and tells me she doesn't have time because she has so much study to do...yet she wastes about an hour a day on facebook and sometimes more on other site like 9gag etc.
Something else I should mention is that when we are apart in the holidays (2 or 3 weeks) she finds it WAY harder than I do to be apart. I do miss her a lot during those times but I can remain happy and productive whereas she gets very emotional and cries almost every day.
I really don't want to break up with her, she is beautiful, intelligent, honest, trustworthy and fun. What advice can you offer me, Reddit?
tl;dr - My girlfriend doesn't mind drinking or smoking weed when we are together, but will act out for days and make me miserable if she finds out I have done either without her. She acknowledges that her behavior is hurtful, but is unable or unwilling to work on changing it. I don't feel that my use of weed or alcohol is irresponsible and I feel she is being irrational. How can I improve this situation?