2 back to back hands... first one, I think I played pretty good... the second, not sure if I got greedy... would you call an $18 raise w/ 4 to a flush and holding the K...

Ultimate Bet No-Limit Hold'em, $1 BB (8 handed)

MP2 ($99.55)
CO ($98.70)
Button ($66.75)
SB ($23)
BB ($57.60)
Hero ($125.95)
UTG+1 ($50.50)
MP1 ($61.65)

Preflop: Hero is UTG with , .
Hero calls $1, 1 fold, MP1 raises to $2, 1 fold, CO calls $2, I calls $2, SB calls $1.50, 1 fold, Hero calls $1.

Flop: ($11) , , (5 players)
SB checks, Hero checks, MP1 bets $4, CO calls $4, SB folds, Hero raises to $15, MP1 calls $11, CO folds.

Turn: ($45) (3 players)
Hero bets $43, MP1 bets $43, Hero calls $0.

River: ($131) (3 players)

Final Pot: $131

he had AK, and I got myself a nice little pot...

VERY NEXT HAND...:

Ultimate Bet No-Limit Hold'em, $1 BB (7 handed)

MP1 ($99.55)
MP2 ($92.70)
CO ($66.75)
Button ($21)
SB ($56.60)
Hero ($193.60)
UTG ($50.50)

Preflop: Hero is BB with , .
3 folds, CO raises to $2, 1 fold, SB calls $1.50, Hero calls $1.

Flop: ($6) , , (3 players)
SB checks, Hero bets $6, CO folds, SB calls $6.

Turn: ($18) (2 players)
SB checks, Hero checks.

River: ($18) (2 players)
SB bets $18, Hero calls $18.

Final Pot: $54

What I didn't understand is why he didn't bet the turn... he had ... if I wouldn't have called, he would've turned his nut flush into $6...

2nd hand I definitely call that. You only need to have the best flush 1 out of 3 times to make it worth the call. At least some people will make that bet with lesser flushes.