boyfriend troubles?

What would you do if your boyfriend smoked weed and got really high when he said he was going to come and see you but he then couldnt because he almost blacked out from how high he was? and you dont like weed or any drugs that are illegal as your birth family were all drug addicts. but you kind of want to try it because life is short and it could be fun and you have no idea what its like until you try it, but another thing you hate is that your boyfriend is only 17? (turns 18 in a few months). He's a great guy, very caring, understanding etc, but this is the main thing you don't like about him - he doesnt do it often, very very rarely, and he knows how i feel about it as I almost broke up with him (mostly as he done weed first instead of coming to see me, which makes me sound pathetic but i mean come on). He argued that he didnt know how strong it was, which is fair enough, but if he'd just stopped and thought...
I've forgiven him. THIS ONCE. But I can't stop thinking about him doing it and that hes underage and that his mum was perfectly fine with it, in fact she came and picked him up because he almost blacked out, but my parents wouldn't have been okay with it, even though im 18 ((
That's also why I cant talk to them about it because they might be like "ooo break up with him because we dont want to repeat the cycle that you had in your previous family" which is why I want to talk about it to you guys and get your opinions. Me and him are very strong, been dating 7 months now. But this is the main thing I can't stop thinking about and it happened last week...
thank youu x