I feel I should completely withdrawing from my group of friends.
Why do you want to abandon your friends?
It's not really the nicest place to be. I did a lot of bad things with them, and did a lot of drugs.
It might be a good idea to leave a group of friends if you feel they are a bad influence on you, but make sure to find new friends. Being completely socially isolated can really harm your mental health and might make you feel worse than before.
Eh I've dealt with more messed up groups of friends, not like drugs are bad.
They might not understand if you abandon them, I think you should be honest why you are leaving.  Since you were in the same position they were in I think you should say it kindly because you don't want to be seen as judgmental.