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