Could my partners drug habit be the cause of my miscarriage

What types of drugs,

But in general, no it would not be the cause. It could be the cause for many other things, and you should consider if this is the type of man you want as a father of your child.

Miscarriage can happen for many reasons. The two primary are:
1). There was trauma to the uterus and foetus which would severely limit the viability of the child. The body cuts its loses and terminates the pregnancy. IE, you fall down the stairs.
2). There is too many genetic abnormalities. The chances of survival outside the womb are limited so the body cuts its loses and terminates the pregnancy. IE, the foetus has two recessive midget genes. A fatal condition. This is usual seen in early pregnancy.

The only your partners drug use could affect a pregnancy is if you were partaking as well or a byproduct was inhaled/ingested from his drug use. IE, second hand pot smoke, or something along that lines. It would be hard for that to build up enough I think.

I think it would be one of the above two reasons. Though I must ask why you're asking this question.