100NL Nit raises me on the flop

PokerStars No-Limit Hold'em, $1.00 BB (8 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: FlopTurnRiver)

MP1 ($105.25)
MP2 ($133.25)
CO ($32.50)
Hero ($97)
SB ($169.50)
BB ($133.60)
UTG ($50.65)
UTG+1 ($34.60)

Preflop: Hero is Button with 5, 5.
UTG calls $1, 1 fold, MP1 calls $1, 2 folds, Hero calls $1, SB completes, BB checks.

Flop: ($5) 5, J, 6 (5 players)
SB checks, BB checks, UTG checks, MP1 bets $4, Hero raises to $12, SB raises to $32, BB folds, UTG folds, MP1 folds, Hero ???

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SB is a 11/4 over 210 hands.

What's your move here?

Bottom set
Unraised pot
Mono-tone board
Check-3-bet
...from a tight-ass opponent

I fold this so fast.

...and I can only ever remember folding a set on the flop once in my life, ask Xianti or Tyson about it.