T.H.
Maybe he's just going through separation anxiety? Do you read a story before nap? I know that helps my little guy. It makes the transition slower and we get a cuddle in while we're reading. I would maybe see if you can get him to use a specific lovie or something that might help calm his nerves. I know he's still young yet, but maybe have him pick out something from the store and tell him it's his special nap/night time animal.
If he isn't really napping then yes, I'd move his bed time up, at least for right now and if he goes back to napping then go back to 8pm. But, if he's overtired that will exacerbate the crying and whining and fighting sleep and will just make it all worse! I'd say if he doesn't nap, go for 7:30 at the latest. I do agree with you that you don't want to get in the habit of sitting in his room with him each time.
Good luck, this is a tough one!