Kristal, this page looks really helpful, particularly the 10 warning signs list
http://www.alz.org/what-is-dementia.asp
what you could do is broach with him about the changes, and ask him to go to the HP for your sake, just so that the possibility of a problem can be ruled out. If you put it that way, he might be willing to go - but the GP will be used to dealing with denial about things like this. If the changes have crept up on him, your husband might not even have noticed them, or be very frightened by the prospect (I know I would be). Tell your husband how much it's worrying you, so that he can think he's going to see the doc to set your mind at rest. You may have to be a bit devious in getting him inside the surgery door!
I don't know how old your husband is, but in England GPs are initiating 50+ health checks. If your practice is doing that, you could ask them if he could have an appointment and they'd send him a letter - that way, it's them initiating the appointment, would that work?