As you are both quite young, I hope this doesnt come across as patronising but there are a few points in what you have said there that I think would be constructive to address. But take my opinion/advice however you will!
Firstly, the most difficult one. You mentioned that he went to Netherlands and tried weed and mushrooms, he’s young, it’s his decision if he wants to experiment with those experiences, your comment that you “thought you made yourself clear” sounds quite controlling, and I would suggest reflecting on those impulses (I know they come from a positive place!) And ensuring that communication and compromise with partners in future is key to a healthy relationship. Likewise, if a partner wanted to control or limit your experiences in life. This may be worded poorly, but point is I would reflect on where these emotions and behaviours may be coming from within yourself and address this moving forward.
With that our of the way, the REAL issue here. My assumption would be that this is an immature person, who was not quite ready enough to handle the experiences of these drugs and has become quickly addicted to the high and the escapism, with no impulse control over himself or his actions. In some ways, it can be beneficial to have these experiences in life now when young, as opposed to later, however, that is only if he can find a healthy way out. Judging by his experimenting with meth, I would say he’s likely past the point of being able to do that without proper medical assistance and counselling.
BUT, that said, HE IS NOT YOUR RESPONSIBILITY TO FIX. It is not your fault. He is living his life the way he has chosen, and that does not align with your morals and values. You absolutely 100% should break up with him, ensuring that you put across that this is not what you are looking for in a partner, set your boundaries, express your concern for his wellbeing, and request that if he is not going to seek professional help then to be careful and safe. But after that, wipe the slate clean and move on.
Yes, it’s extremely difficult emotionally, and you may feel like you are abandoning him, but you are not. He has made his choices and they have diverted from yours and he is, once again, not your responsibility!
Better that way, in the hopes that he sees the error of his ways sooner and seeks help, because the alternative is you being dragged down with him. You need to be clear, firm, and set your boundaries that it is over, and BREAK CONTACT FOR AT LEAST 6 MONTHS. Do not get caught in the spiral, look after yourself and stay healthy!
I would be surprised at the absolute stupidity of that, voting for the absolute corpo party in some bizarre protest, but you guys already voted him in for a first term so nothing is really surprising when it comes to the US anymore.