Villain in this hand is a multitabling regular. Not many more reads then that. 3bet a decent amount.

a) What do you think of my turn bet size?

b) Do i call now?

PokerStars No-Limit Hold'em, $6.00 BB (9 handed) - Poker-Stars Converter Tool from FlopTurnRiver.com

UTG+1 ($715.05)
MP1 ($600)
MP2 ($570.65)
MP3 ($636)
Hero (CO) ($888)
Button ($276)
SB ($627)
BB ($487)
UTG ($679.05)

Preflop: Hero is CO with 6, 8
UTG bets $18, 2 folds, MP2 calls $18, 1 fold, Hero calls $18, 1 fold, SB calls $15, 1 fold

Flop: ($78) 10, K, 3 (4 players)
SB checks, UTG checks, MP2 checks, Hero bets $60, SB calls $60, 2 folds

Turn: ($198) 9 (2 players)
SB checks, Hero bets $88, SB raises to $549 (All-In), Hero