Most highschool sweethearts don't last and it has nothing to do with drugs and addiction. Some people begin to mature and some people do not. Priorities change or remain the same.
You have career goals. You are in school. You work. You seem to be taking responsibility for yourself.
He's addicted to drugs and that's his priority, right now. He's unemployed.
He's not attending school. He's involved in criminal behaviors. In other words he's irresponsible.
Does it make sense to focus on your own situation and triggers. Being alone is not the same thing as being lonely. What is it you fear?