My husband and I have a wonderful relationship, however the issue of Niddah is difficult for him to come to terms with. In particular, during the period of my Niddah, he feels extreme sexual tension that needs to be released. Is there an halachically acceptable way for him to release this tension?

I am pleased to see that you and your husband keep the laws of niddah. This will definitely strengthen the connection between you. If your husband finds it difficult to keep these laws, he should learn the laws of niddah and get to the point that he understands the importance of the laws and the framework of them within the marriage. Kol Tuv