My husband insults my parents to me and then is nice to their face?

My husband repeatedly has made awful comments regarding my parents. I am an only child and my parents have been good to me so I am very close with them. My dad does have a drinking problem so he is an easy target. It is a subject that I am very sensitive about. He will say mean things about me and about them over and over. When I try to address it he just says quote "let it go" but it really hurt my feelings. Then he will go and be nice to their face like he never even said those things. I have NEVER said anything disrespectful about his parents. This is just a small issue that just happened. We have numerous problems and we are already on the verge of divorce. And I have about had enough...