Cooling off time is a wise idea. Otherwise things get said in the heat of the moment and most of the time it makes things worse.

I would back off a bit...and if he calls you.....then go from there. But at some point in time you do need to find out if he is doing anything....and if he cares about you he will be honest and not offended. Being that defensive kinda raises some red flags. If he wasn't doing anything....then it shouldn't be a problem for him to say.."No, I don't do drugs!" and then the subject would be dropped because he can say it without hesitation or feeling offended.

If you want you could call him, but honestly I think the issue won't be resolved and you might find yourself in this exact situation in a few weeks, a month etc. The more you ask him....the more pissed he will get etc. Then he will run off again all upset. I would let him come to you. If he truly does care about you....he will. If not then you know that drugs are more important to him .....and honestly its best not to be around that.

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Appreciate the good times and learn from the bad times....