My husband has and exposed nerve in his tooth, is there anything I can do to help make him more comfortable before he goes to the dentist?

Several things. The most important thing to do here is to get to a dentist quickly to prevent nerve damage or death. In the meantime taking an anti inflammatory such as Ibuprofen can help the inflammation and applying some clove oil to the affected tooth also may help the pain until he sees the dentist.
Temp Fill and Meds. Try a temporary dental filling material containing clove oil available at the drug store. The clove oil will calm the nerve. Follow the directions on the package. If your husband is not allergic to Ibuprofen (advil, motrin), have him take 600-800mg (3-4 tablets) every 6 hours. If needed, he can take 2 extra strength tylenol (acetaminophen) (1000mg) between the Ibuprofen doses. Consult with his dentist asap!
Maybe. Give him 1 regular Aspirin with 1 regular tylenol (acetaminophen) along with an antibiotic. However he needs to get to the dentist that can actually treat him (not one who delays treatment and needs to refer to another dentist).