TIFU by lying to my gf about my weed usage

I've been with my gf for 3 years now and since the beginning she knew I smoked somewhat regularly weed. I've had long breaks of not smoking but I never knew how to talk with her about how much I do it and when, specially cause I know she isn't the biggest fan about it but tries to be comprehensive. At the beginning, we decided that I could do it whenever I liked but just make sure to tell her (we don't live together and likes to be aware of what im up to), but since the beginning of this year I've been in a depresive episode in which I started smoking more and without caring when or for what, staying up late just to smoke or going on walks or runs just to do it, even when we had plans and faked I wasn't high. Thats when I stopped telling her, because I knew she would be worried and wouldn't aprove of my excessive usage, so it's been a snowball of lies from there on.

I would do it all the time and not tell anybody knowing im not in a good mental place, but acting as if nothing was wrong. I took really good precautions so no one would find out (using eye drops, always having water and gum for my breath, disinfectant for my hands, keeping all my stuff in sealed packages so I never smelled) and it worked out pretty well, but with time I started being careless and even my brother found out.

But yesterday finally all the thruth came to light. She found a post I did in r/weed about all the stuff I've bought recently and lied to her face saying it was all old stuff (she believed I haven't done it in a couple of months and going out and running was me taking care of my health). She said she believed me and was just scared I was hiding things from her :( but I kept lying and saying everything was okay. Later that night we where going to meet up and I don't know why but I smoked before hand and obviously she noticed when she kissed me. At that moment she joined all the dots and confronted me about all the lies I've told her this year, saying I broke her trust and that she doesn't know how we can continue after this.

I don't know why I did what I did, I know im a shitty partner that is afraid of confronting the thruth and now I fucked up the best, caring and loving relationship I've ever had. I know I can't ask her to give me another chance if her trust is broken, specially if I don't start to take responsibility of my actions and solve the problem from its roots. Going to therapy or rehab isn't enought, but I just don't want to accept that everything is over.

TL;DR: I lied to my gf about how much i've been smoking weed, she found out and now I don't now what to do, I broke her trust and we might broke up