First off I would drop this girl like a bad habit (no pun intended). As much as you may think you need her around, when you can get her around, you really don't. Once you get that break away from her the glamor of it wears off and you'll be over it.
Second I would find something to be passionate about other than drugs and wrap yourself up in it, distract yourself as much as you possibly can (I know that is way easier to say than do), but if there is anything else that you have fun doing than do it, and do it a lot and you will realize there are other things that life is worth living for. Even if you are still in mental agony knowing, and especially seeing that there is some light down there at the end of that long ass tunnel can keep you going.
Why don't you try dropping your dope habit and save the money you would've spent on that and take a trip to somewhere you've always wanted to go, and go alone. Going somewhere far away and being out of your element can put a lot of things in perspective, not to mention it's very peaceful. To be with yourself. It sort of reminds me of the Buddhist retreats people go to.... days and days of silence, no talking, no noises, just complete silence. It really only leaves you living in your own head and that is some serious shit. I don't know, I think you would really have to be ready for that one because I know how hard it is to live in one's own head with out the silence and distractions but who knows it could work for you. Good luck and I hope shit gets better for you.