I agree with bb's advice that you should tell him directly that you don't want to discuss his ex anymore, particularly when you're having quiet time together. It might have been more appropriate as small talk in the car, or while you're both doing housework together, etc.

I disagree with shezbut in that i think people CAN be essentially blameless in an abusive relationship. Not saying that he was perfect in his previous relationship, but that doesn't mean that he contributed to the abuse either.