How do you make your husband accountable after learning he cheated and impregnated another woman?

The only way to make him accountable is to force him to face the consequences of what he's done, i.e. divorce. If you stay with a cheater, you are teaching him that there are no consequences for his actions, that cheating on you is ok, and that your feelings don't matter. Your so-called husband isn't sorry he cheated, he is sorry he got busted. He will keep cheating.