Hi,
Well when he bets so small on the flushing turn it's very often because he's scared so you're probably ahead, but at the same time he's not so likely to call a raise because it looks strong on your part. At nl4 i'd still make a small raise on the turn because people have a hard time letting go of top pairs and 1 card flushdraws, so i'd go with something around $0.9.
Obviously if he 3bets it's disgusting because it doesn't make too much sense because of his small/scared bet in the first place, but you probably have to give it to him anyway unless you think he can do that with a worse Ax with a heart.
Hope it helps.