Heck no....you're not bad. This is a consequence of his drug use. He has damaged the relationship and you are doing what you need to do for your own psychological and spiritual well being.
I truly believe that the motivations that drive us are what is really important. If you aren't taking his calls because you want to punish him.....those may not be pure motivations. If you aren't taking his calls because they cause you stress, anxiety, fear, guilt, etc. then your motivation is self preservation.......pretty good reason not to take his calls.....don't you think?
Keep taking care of you......
gentle hugs
ke