I'm sorry that you're going through this. You definitely haven't failed as a mother, I promise you.

As someone who has studied the psychology of drug addiction, I can tell you that there are a lot of external factors that contribute to drug use and addiction, such as demographic (according to WHO in 2013, drug use is higher amongst males in low to middle income countries - I see you live in a poor county), other medical comorbidities (e.g. is he depressed? Does he suffer from anxiety or other psychological or physical conditions?), associative learning (are there any other drug users in the family/friendship groups?) and also the individual (the brain elicits strong neurochemical rewards and triggers aversive reactions when drug use is discontinued).

In treating him, it is also important to note that many people who use drugs continue to take them to avoid the negative symptoms of withdrawal. He may not necessarily want to be taking it - like you said, he does feel ashamed - but he most likely can't make himself stop because he knows that he's going to have cravings or bad physical symptoms if he stops taking cocaine.

The best way to counteract addiction and drug use is to do through interdisciplinary therapies that amalgamate medication and counseling. A variety of cocaine cessation treatments are available, including pharmacotherapy, cognitive behaviour therapy, counseling, support groups, and the like. Behavioral rehabilitation on its own has shown to be unsuccessful.

I thought I would provide you with some facts and info that may help you in some way. I agree with other redditors here that you should try and convince him to get into therapy or to see a doctor - for both his and your sake. Also, don't give him any money, and if he tries to manipulate you into it, don't give in. You will only be enabling him. Moreover, keep a record if that info you found about the man in his 30s - you may need it later if things continue to escalate.

Good luck.