What did you put him on when he called your raise on the flop. That raise usually folds the table. When it doesn't, the first thing you do is look at your kicker. an 8 is a weak kicker.
Given the weak kicker, you should have planned your next two bets so that you got to the river without putting too much money in the pot. That's how i'd play it. ie Turn $15, and River check call or 1/2 pot bet.
Discretion is the greater part of valor.