99 must be more optimal to go allin when he bets. There are multiple combos of hands you can go call flop, check back turn och raise allin as a bluff on the river. Especiallly Qh hands. JT, KQ with one hearts and more. In hindsight, now that you saw his hand, do you think he would have called? Your set is so disguised, I would have put my money in, and sometimes he has the flush, but I dont think he often check backs the turn with the flush.
Various ways during the years (I played my first hand in 2010). In the beginning it was just forum discussions and books. Then Coaching, websites such as RunItOnce/Upswing and a lot of study on the solvers.