You wrote the email (been there, done that, regretted it the next day), had the relapse (likewise, familiar, too), and you're right - there's no weakness in feeling pain. But to quote James Ellroy, vis a vis his mother's murder, and relationship breakdowns certainly leave bereavement in their wake: closure is bullshit. Sometimes a necessary, auto-suggested kind of bullshit, but I wonder sometimes if all these spatial metaphors we use for emotional trauma and recovery - 'getting over it', 'closure', 'moving on', aren't based on a false premise. Time and space may be identical in a metaphysical, higher sense: day to day, emotionally, they're not. It does sound like you were invested in the relationship to a greater extent than your ex; I've been there, and though I was the one to leave, it's been over two and a half years, and I still find her name on my lips everyday. And yes, I asked 'why?', why the inequality between us, why was all the support and affection I gave her not enough to move her to reciprocate: and it was an unfair question, if an inevitable one. How the fuck could she know? We tell ourselves stories about our motivations, reasons - but we make them up as we go along. She won't necessaily know why, and if she does, may not be able to admit to herself, or you. In the end, it makes no difference to the situation you're in.
As other posters have said, meth is not your friend here, and nor are H and benzos: I flipped from two destructive relationships into a pharm painkiller & benzo habit I'm still in treatment for, and it's just compounded the sense of lost time and self-disgust/hatred. This seems to be a common pattern for men who put too much of ourselves into relationships with women who are fundamentally more independent - and perhaps, inclined to take more than they give - because we put in resources, strength and energy that we need for ourselves.
I know the pain must be immense, and won't hit you with the platitudes, but take care of yourself man, know that I'm one more Blueligter who feels empathy for the pain, and don't beat yourself up (that includes hitting the pills and spike and crystal)for having sent the email. Sometimes we need to howl like that - and do so knowing that it's going to nix any vague chance of reunion. Given the state she's left you in, do you really, really, want her back, so you can go another fifteen rounds? It sounds like the kind of relationship that turned quietly toxic, without either party fully knowing why - there sometimes are no useful explanations. Sure, you crave her: but like a dug you've burned out on and can't kick, it's acraving which might, if satiated, produce not the old high, but only increasingly dehabilitating and painful side-effects. Be as clean and as gentle with yourself as you can, and PM me if you want to exchange stories or just need to talk.
WW.