It's heads up sb vs bb, he's not raising you on just AA or KK. You probably have 2 live cards and are getting 3:1. Just continue if you pair something or hit a draw etc... If you fold here, your inviting him to do that again. I think your mistake was post flop. You should have bet into him. Your bet could mean a lot of things, it could mean top pair trying to protect ur hand, a high spade that your willing to semi-bluff at. You need his money on the flop now because the 4th spade will kill your action. If the fourth spade comes he will play correctly against you. He will call or probably raise when he hits his flush because it will be higher then yours probably and will fold thinking that kid got lucky again and hit his flush draw. Now, he may raise you on the flop and then you can 3 bet him. You got lucky that no spade hit the turn so you could check raise him with the flush. Sure you won an extra small bet but your going to lose a big bet when the spade comes and maybe only win his bet on the flop if a 4th spade does hit the turn (check, bet, call... check, check.... bet, fold)