Because you have an addiction. Addiction is not about choice (it’s not like choosing whether or not to have an orange with breakfast - I can choose to have an orange or not; it’s a choice that I can do or not do, no problem - but addiction is not about choice: an addiction is deeper than choice). You need help - we all do (no one recovers from addiction alone) - and you need to get both physical and mental supports.
Have you spoken with your doctor about your depressive feelings? There is often something that can be done; take some time to ask your doctor and see what is possible. I found my depression really inhibited my action before I started to work on it.
Look into pathways to recovery. There are many different ones but they all involve learning from people who have more knowledge.
Welcome to Talking Sober!