Bottom set vs. flop all-in

[GoCubsGo]

Villain is 17/2/2.5 after only 44 hands. Hasn't done anything special.

PokerStars No-Limit Hold'em, $0.50 BB (9 handed) converter

MP3 ($49.10)
CO ($85.80)
Button ($14.50)
Hero ($49.70)
BB ($59.60)
UTG ($53.85)
UTG+1 ($53.85)
MP1 ($20)
MP2 ($29.50)

Preflop: Hero is SB with 7[img]/images/graemlins/diamond.gif[/img], 7[img]/images/graemlins/club.gif[/img]. MP1 posts a blind of $0.50.
UTG calls $0.50, UTG+1 calls $0.50, MP1 (poster) checks, <font color="#CC3333">MP2 raises to $2</font>, <font color="#666666">3 folds</font>, Hero calls $1.75, BB calls $1.50, UTG calls $1.50, UTG+1 calls $1.50, MP1 folds.

Flop: ($10.50) 9[img]/images/graemlins/spade.gif[/img], 7[img]/images/graemlins/heart.gif[/img], T[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(5 players)</font>
<font color="#CC3333">Hero bets $7.5</font>, BB folds, <font color="#CC3333">UTG raises to $51.85</font>, UTG+1 folds, MP2 folds, Hero?

At the time it seemed like a clear fold. Now I'm not so sure. Could have been an overpair, but at the time I was thinking higher set or Ax [img]/images/graemlins/heart.gif[/img].