Im 15 and was going out with an 18 tahun old we both have addictions to certain things but he berkata 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 anda had,and a potential " heartbrake"
If it's been 3 weeks already there might be serious problems.
*He might have decided to ignore anda 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 tarikh 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 anda surprisingly:'Ohh Im not really in a good mood for relationships,maybe seterusnya time?'
atau something related to it.
my Nasihat for anda 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 seterusnya step,If he just finds a lame excuse and the seterusnya moment dumps you,FEEL HAPPY!
he Lost something he didn't worth,and say/do anything that cheers anda up!
If he feel's sorry and apologizes to anda explain him what anda understand about Cinta (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 sejak happiness and pain-
In your case :-happiness was shared through both of anda butonly anda endured the pain.