You're going to need a reason to change if you actually expect to stick with it. Since addiction hijacks the reward system in the brain, you're going to have to think meta-cognitively here. Even though you WANT to change, you're going to feel strong desires not to because your brain is conditioned to feel that reward.

New friends who are bettering themselves as well or are working toward some productive goal are important. If you don't have a degree and your life is really in tatters, consider going to university (**edit to add: don't hang out with the party kids. Find the passionate nerds who are still fun to joke around with. Studying in a group, even if you're all just sitting together working on separate things, is a lot easier to motivate yourself to do than studying alone).

I've found it very helpful to cultivate a love of learning for it's own sake, and to foster a natural curiosity in yourself. As much as like-minded and determined friends will help, if you don't have those self-directed goals, it's not going to last. And it could be dangerous to try to fill that void with a romantic relationship right away.

I'm not going to lie. You're going to have to suffer through the cravings, depression, boredom, anxiety, etc. But the longer you stick it out, the weaker those negative feelings will get.

The more you do drugs, the more you will want to do drugs. So just hold out as long as you can, don't get demotivated when you fuck up, because no matter what, if you stick to this, your drug use will be on a net trajectory downward.

You've got this bro. Godspeed