The thing above love is that the characteristics we admire in one person belongs to many people. So if you love him because he's sweet or whatever, there are people out there who are just as sweet, if not sweeter. He just happened to be there at the right place at the right time to make you feel like he's the one for you. I mean, he's not. At least currently he's not. You must ask yourself why you love him, not as he was before when you fell in love with him, but why you love him now. Whatever reasons you find, ask yourself is it worth staying for. If it is, then stay, if it isn't then leave. The relationship itself isn't good. As soon as it becomes on and off, it's rare, if even possible, for it to ever become good and stable again.
Or perhaps you may choose to focus on the future. What he may be like, what he may become. If you vent your frustrations and feelings to him, and make him see stuff from your perspective, then surely he would understand and stop upsetting you and that. At least that's what he would do if he valued your relationship more than having drugs. But it is imperative that you figure out why he acted on the way he did, and ask if he will ever do it again. If he learns his lesson, then he's worth it, if he doesn't then he isn't. Rn you being so sad and down, it's not what a relationship should be about. Figure out his intentions, and give that more importance than his actions. If the intentions are good then he's just going about the wrong ways, cut him some slack