Just finished Civil War quests again (favoring Empire, if the title didn't make it obvious). "Finished" as in killed Ulfric, listened to Tullis' little speech, and journal entries completed. I fast travel to Whiterun (from Windhelm) and who appears at the gate?

Hadvar, and he's following me. He says things like "Hello friend" if I interact with him, but otherwise has no dialogue or options for interaction.

If I fast travel ANYWHERE else (random locations, other cities) he's not there, but whenever I go back to Whiterun, he is, and always follows me. I reloaded and it does the same thing, except this time I fast travelled to other places before Whiterun, but he still shows up at Whiterun. He won't follow me into buildings or outside the city. If I attack him, he's still essential and so he won't die (Whiterun guards will react and come after me; Hadvar will also fight me back).

I've done the questline a bunch of times and never seen this. Did he decide to retire to Whiterun and is just REALLY friendly? It's not a major issue, just kind of weird.

EDIT: And I've checked other threads that talk about the same problem, but none of the "fixes" seem to work (saving, reloading, and he'll leave, etc.).

This is a known bug that can happen to some players. Maybe he likes you.

you can fix this bug by attacking him and then yielding.

Restarting the game made him stop following me.

Happend to me too. I just figured it was a glitch, and ignored him, and he went away..