You cannot let go. You don’t watch him, you need to watch yourself; then you can let go. Otherwise, you always pay attention to him, and then your anxiety and worry increase.
Later, every time you watch your husband, this anxious and worrying mind will arise; the pattern is already there. You allow this pattern to happen again and again; then you always look at your husband with a worrying mind because it has become a habit. So, next time you don’t watch his face. Whenever you see his face, you come back and pay attention to your own mind.
So, come back, come back, and come back. He can do his job; you do your job. He and you are different. He is he and you are you.
If you want to let go, you need to watch your mind. Otherwise, if something happens, you’ll have more worries and no idea how to help.
If you are more relaxed then you can find a way to help your husband. You can think of a good way; so take care of yourself first.