You could make a witch bottle and bury it on your property. That would at least help keep him away from your home. As for away from your husband you could make an amulet and give it to him to wear. But keep in mind that if your husband really wants to associate this person, you cannot stop him with Magick. He will have to make the conscious decision to change and stop doing those things for the sake of his family. You cannot change someone who does not want to change. You can't really make someone do anything.
My advice would be to talk to your husband, before anything else. Magic rarely, if ever, has any real lasting effect on a person's free will. If he does not understand that you want him to disassociate from his dealer, no matter how successful of a working you do, he may choose to continue doing so.
If you insist on doing something, the simplest thing I can think of is a freezer spell, though that is more often used to slow the actions of a snarky coworker, for example. But it is one of the very many jar spells used in folk magic, employed because they are simple and direct.
You might also want to symbolically cut a cord between them, or do a binding-away ritual of sorts. I wish I knew a formal name for either, but there are numerous options out there.
I have recently read an article about separating an attempting interloper from one's lover. I could see how a thorough modification of the working, starting with color correspondences, through the songs and chant used, could be just as useful for your purposes. Here is a link to the blog (no affiliation on my part):