Villain is completley unknown. His line kinda scared me into believe he could have a bigger flush, but is this just weak? Sh0uld I re-open the betting on the river?

PokerRoom No-Limit Hold'em, $1 BB (4 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: FlopTurnRiver)

SB ($210.50)
Hero ($211.40)
UTG ($116.15)
Button ($45.50)

Preflop: Hero is BB with 5, 9.
2 folds, SB completes, Hero checks.

Flop: ($3) Q, 3, J (2 players)
SB bets $1, Hero raises to $4, SB calls $3.

Turn: ($11) 6 (2 players)
SB bets $1, Hero raises to $10, SB calls $9.

River: ($31) 8 (2 players)
SB bets $1, Hero raises to $25, SB raises to $49, Hero calls $24.

Final Pot: $129