Am I immune to addiction?

Habit is an interesting thing, it can both encourage you to use and keep your use within limits which you set. So your habit has settled in to being a regular thing and this supports your continuing to use. If you found yourself breaking your habit, then you might think that you had to stop, which is why keeping your habit helps you to continue to use. There will not be a problem until your level of tolerance begins to rise and you no longer get the results you were getting from a regular amount of substance. It would also be useful to look at what other substances you are using. What is the alcohol mix, alcohol might mask the need for further amounts.

You will have seen that it took a time to progress from irregular to regular use, in the same way it is possible that it will progress slowly to daily use. You do not tell me whether you inject or smoke heroin. Many people smoke then progress to injecting.

No-one is totally immune from the gradual physical addiction, but certain things will help to keep it stable. Having a regular pattern of life and of when and how you use. Having supportive friends and family and not suffering any traumatic events in your relationships/employment will all help. Using heavy amounts of alcohol with it is dangerous in itself, as well as impinging on your control.

I would not be telling you what to do, but I would be wondering why you have to knock yourself out of the picture for much of the weekend by using heroin. I suspect it would be useful to see whether there are aspects of your life which are needing attention but are not getting it because of your using. Look to see what is not happening in your life, and progress that and then you will see the real reasons why this is dangerous and why it is getting on time you chould be thinking about cutting down and moving into a more productive phase of life.