Winning Poker Network (Yatahay) - $0.05 NL (6 max) - Holdem - 6 players
Hand converted by PokerTracker 4: http://www.pokertracker.com

MP: $6.45 (VPIP: 24.29, PFR: 12.86, 3Bet Preflop: 0.00, Hands: 71)
CO: $5.85 (VPIP: 21.74, PFR: 13.04, 3Bet Preflop: 0.00, Hands: 23)
BTN: $10.61 (VPIP: 23.17, PFR: 15.34, 3Bet Preflop: 6.15, Hands: 170)
SB: $2.41 (VPIP: 21.74, PFR: 17.39, 3Bet Preflop: 0.00, Hands: 23)
BB: $5.31 (VPIP: 61.90, PFR: 31.75, 3Bet Preflop: 0.00, Hands: 64)
Hero (UTG): $5.26

SB posts SB $0.02, BB posts BB $0.05

Pre Flop: (pot: $0.07) Hero has Ks Kd
Hero raises to $0.15, fold, fold, BTN calls $0.15, fold, BB calls $0.10

Flop : ($0.47, 3 players) 4d 3c 9s
BB checks, Hero bets $0.29, BTN calls $0.29, fold

Turn : ($1.05, 2 players) 8s
Hero bets $0.73, BTN raises to $1.75, Hero ???

BTN is the most solid reg I've seen at this stake lately. He's opened up 89o UTG, but my notes don't have him 3betting anything other than QQ and AA. I mean, is he doing this with a flush draw, and isn't it a really good spot if he is? He's repping the set, can continue to do so on the river, and still might complete his flush. If he has the set, I'm done. How do I proceed here?