I've had to cut my son off from support, I tried helping but he got out of hand, even the lady at the store stopped and talked to me and said she felt for me, understanding herself, he own son hasn't talked to her in years she said. He was shouting in the store that I'm a fn ******I can't give him money, he threatened to buy Fentanyl and I won't give him the opportunity. He was showered, so he still has support from the community in town here, albeit it's not much.
The part about your son's behavior sounds really hard. I have been in "recovery" for over 15 years and only continuously abstinent for 3. Been through the entire continuum of care from "white knuckling it" on up to inpatient rehab and private addiction treatment. So I would expect myself to know how to do this "boundaries" thing and able to determine the border between offering loving support and care of a close relative, vs enabling their self (and sometimes other)-destructive behaviors. Had a similar pattern with my niece, who AFAIK is still struggling with IV opiate addiction. Similar issue with my sister presently, who is spiraling due to grief and not letting anyone help. So- yes it is heart-rending and feels extraordinarily guilt-inducing, like you are overriding your instinct to care for him.
As per my developmental psychology course, young children tend to bond most strongly to the opposite-sex parent, so that is why we have "momma's boys" and "daddy's girls" So the bond between you is one of the strongest bonds of human nature. Which is why it is so brutally painful... but for me - I have had to take the long-term perspective, as in "will I feel like I did the right thing 1 or even 5 years from now?" People don't change until they are in a situation where the pain of the status quo exceeds the perceived pain of change. This is the more articulate description of having to "hit bottom."
Not everyone bottoms out at the same point, but everyone has to reach a point where it's hurting so bad and destroying so much that one is willing to do anything to change. Based on your previous posts I have the image that he is past the point of enabling though, and when I read the posts about your son, I make up an image of someone who is like my niece, i.e., any material resources contributed will allow the addiction to continue snowballing. Because if I buy her clothes, she has more money for drugs. If I drive her somewhere, she didn't spend money on fuel that she can now spend on drugs, and so on. This is based on empirical observation; she only got worse when we tried to help. But I imagine it is far more difficult and painful for you, because he is your son. I am not a parent so it's not possible for me to put myself in your position. I can put myself relatively close though, and can only imagine how tough it must be to stick to your guns.
If I could I would like to remind you that you are strong for doing this, and I don't know if he will get better, but it very much appears to be that when you help him he tends to go off the rails again.
I hope that helps. It's more just my reaction than advice, so if it doesn't match your experience please disregard it. Sorry I'm just really vulnerable and raw right now.