Im 15 and was going out with an 18 سال old we both have addictions to certain things but he کہا he wasnt in a mood for a relation ship and he and i would get back together when he was and it has been 3 weeks what do i do?

Well,In my opinion this proves,lack of interest in continuing the relationship آپ had,and a potential " heartbrake"
If it's been 3 weeks already there might be serious problems.
*He might have decided to ignore آپ and try another relationship.
*And though For many people Age doesn't count,there are still some people who care about that problem.He might have wanted to تاریخ someone his age.
*You also mentioned that 'He wasn't in a mood for relationship"
I really think this guy doesn't worth you,
In a relationship both should decide and talk about it first,not announce آپ surprisingly:'Ohh Im not really in a good mood for relationships,maybe اگلے time?'
یا something related to it.
my advice for آپ is to talk to him in the first place,tell him everything and make him observations! telling him how much this annoyed/irritated you.
The اگلے step,If he just finds a lame excuse and the اگلے moment dumps you,FEEL HAPPY!
he lost something he didn't worth,and say/do anything that cheers آپ up!
If he feel's sorry and apologizes to آپ explain him what آپ understand about love (ofcourse don't be so romantic...talk normal language :) )
And make him understand it's the last time you'll ever wait for him that long without knowing any news from him.

-Love is always accompanied سے طرف کی happiness and pain-
In your case :-happiness was shared through both of آپ butonly آپ endured the pain.