1. Of course, but most likely the most obvious is giving thanks that your husband has a job. This is the number one most positive aspect of someone being considered essential.
2. Are you resenting the concept that he is more needed than you, more desired than you, more essential that you etc?? If this is the case, this is rooted in your own developmental Psychology.
3. Are you missing him because he must isolate without you or is spending several hours away from you at a time and you are worried for his life? This is not uncommon however researching the current prevalence rates of COVID-19 is a helpful practice. In a time like this, overworring about a situation is not going to improve anything. You may also want to research mind Healthy Body and soul connection or the Power of Now by Eckhart Tolle or The Law of Attraction.