I honestly feel so ashamed and don't know what to do with myself.. like what the fuck is wrong with me
You're just a human. It happens. Nothing is wrong with you necessarily. You are just handling some type of internal discomfort, or replacing an external comfort for something that works faster to rid yourself of negative emotions rather than actually working through whatever it is that's troubling you. This is why psychotherapy can be beneficial for some people who have addictions or addictive tendencies. Most therapists are kind of shit though, so good luck there. My suggestion would be to use the psychedelics as they were intended to be used originally, and use them to find yourself and figure out why you are choosing addictive/dangerous substances instead of choosing to heal from whatever is bothering you so deeply however that looks for you. Maybe you will gain some insight into what is
causing you to make this choice again and again with proper set and setting. Set your intentions going into the psychedelic journey, and be sure to write down anything that comes up so you can revisit it later.
It works if you want it to, and if you choose to go that route there are recovery groups for people that decide to handle their addictive behaviors in such a way that meet both in person and online. Not sure if you are in Europe or the US or Australia or wherever else you may happen to be, but there is a European/UK meeting I know of online as well as many US meetings. However, anyone is free to join regardless of locale. It helps to hear others that choose this route's experiences because it opens your mind to new ways of healing more in my experience.
Now, in the meanwhile, maybe explore safer alternatives to the substances like
@3DQSAR suggested. For the alcohol/downers like GVL, maybe try phenibut (or maybe even baclofen or an anti-epileptic depending on what you think/find works out best for you; its your mind and body) if you can get it (or the other substances I mentioned) while you work out why you continue to harm yourself just to feel better and what you can do instead. There is also SMART Recovery which is a global thing as well. LOADS of UK groups, a handful of USA groups and AUS groups as well. They help you develop tools to handle your habits, and there is no need to quit using right off (or even ever really if you find you don't want to) with either.
Anyway, I wish you the best. Addiction sucks.