I dunno what to tell you here. I'm not sure there is any specific good advice as to what to do in a spot like this. I'll tell you the things that I would focus on though:
He's only raising 8% of hands preflop so this fish is likely the type who is not happy to put a lot of money into the pot by raising unless he has something pretty good. Given that, you did say he had a high AF and that he has raised c-bets previously, so that original read might not necessarily be true.
Given he raised your 5 to 12, I'd generally expect most fish to raise smallish on the flop with a 5 and bigger with a flush draw. This is right in the middle so its hard to tell.
Barring any other reads I probably just look at this spot and think "well, this guy is very prone to putting a lot of money in the pot by me betting and him calling, and additionally he's probably less likely to raise to try to bluff me so I suppose I can let this go and wait for another spot". But if I already thought he was getting out of line I'd never fold here.