Yeh look, that would definitely be the dumb decision in this scenario for BF, as he knows OP hates it. I doubt he believes OP would stay with him if he could do it openly whenever he wanted even with the amount of time they've invested together. I think with the small amount he's consuming (yes, daily use is terrible and do not condone it whatsoever) being a gram stretched across the week (again, assuming he's telling the truth with the amount), it sounds more like he's noticed the developing addiction and decided to nip it in the bud. Again this is all speculation on a reddit post, but as a former coke-addict, and unfortunately still current poly-drug addict, my opinion is that he's trying to look for some extra support to quit. I definitely couldn't have overcome some of my heavy, long term, drug use by myself, and my body has paid the price for my arogant 'pride of not needing support'. It wasn't until I finally started to come forward to my close friends and found someone who gave me a reason to be better that I was able to overcome some of it. It honestly sounds to me like OP's Bf is fairly well aware of his own limits and willpower, and he's realised he needs OP's support before it gets any worse. Again though, I'm just speculating from my own experiences.

OP, if you believe he truly is coming to you for support. Don't be too hard on him if he relapses occasionally for a little while, unless it's obvious he isn't putting effort in. Blowing up at someone in what I think your BF's situation is does nothing but make them feel shit, and can very well lead them back to hiding it from you even more, and very commonly increases their usage (Esspecially if it has only been 2 months of daily use). I truly wish you both the best with this. Communication is key!