Feeling overwhelmed

Ive had a problem with alcohol for many years and for the last two years I've had a chronic pattern of binging on meth every 3-10 days. It has caused a lot of problems and makes it extremely difficult to function and interact with people. When I come down I get very depressed, anxious and ashamed. I just got a really good job opportunity as the head pastry chef at an upscale restaurant. In the short period I've been there I've come into work strung out (and intoxicated to help cope with the anxiety) about 4 times in 3 weeks. I know its not ok and Im pretty sure the chef is fully aware of what's going on and seems pretty disappointed in me. I feel so guilty and ashamed and my confidence is so low I can barely think straight or do my job. I want to get sober and healthy and prove that I can do the job but I already feel like a failure. It feels so overwhelming dealing with this addiction and having to live up the the expectations of the job on top of it.