I think my husband has early onset dementia. What should I do?

And, before you visit the doctor (and have an official diagnosis) I would get paper work in order. Health care proxy? Will. Financial POA? You may need a reason to do that so figure that out first! (A college friend whose partner had a stroke and nothing was i order, for example).
Do you know where all of the important paperwork is? Bills? financial statements? etc.

Get him to his doc. Do not mention memory problems to hubby. Rather talk to doc before the appointment for a heads up. Hubby would most likely not agree with your diagnosis. Do not put yourself in the position of starting an argument that will go nowhere. We have seen it time and time again on this site.