Can a landlord evict me immediately if I was arrested for drug possession even though I have a medical marijuana card that makes it legal and charges will eventually be dismissed?

Have you breached your tenancy agreement? Simply being accused of a crime (and then later released without charge) doesn't sound like it's breaching any contractual obligations or understanding.

But there may be technicalities like "smoking in the house" - no matter what substance, that he may be using as grounds for eviction.

Get him to formalize everything and put his qualms on paper. This will give you evidence if the situation escalates to court.