Your husband has a yetzer hara like every other normal man and he will be tempted like any other man is to watch inappropriate things. The important thing for you to know is whether he at least acknowledges that this is something he should work on, but not that he should be perfect all the time.
Therefore, you should put your foot down to express your concerns, but at the same time you should offer your support to your husband in his fight against his temptations.