maybe he was having a stroke?
I think it's important to focus on what you want out of life and figure out what kind of behaviors you find acceptable and how you will allow people to treat you. It's up to you to draw boundaries and enforce them. No one is going to do that for you.
So whether he is using or not using becomes less important than how he is treating you. If he's an addict he will deny using coke until he is blue in the face. Even if you catch him redhanded he will still deny it. That's why you should trust your instinct and focus on behaviors.
But if your not willing to make any changes or enforce any boundaries, then what difference is it going to make whether or not he's using.