I knew I was beat but I couldn't get myself to hit the fold button. Should I have bet out on the flop instead of slowplaying?

Ultimate Bet No-Limit Hold'em, $.25 BB (5 handed)

UTG ($23.50)
MP ($10.05)
Button ($19.15)
SB ($15.85)
Hero ($24.50)

Preflop: Hero is BB with , .
UTG calls $0.25, 1 fold, Button calls $0.25, SB completes, Hero checks.

Flop: ($1) , , (4 players)
SB checks, Hero checks, UTG bets $0.25, Button calls $0.25, SB folds, Hero calls $0.25.

Turn: ($1.75) (3 players)
Hero checks, UTG bets $0.25, Button folds, Hero raises to $2.5, UTG calls $2.25.

River: ($6.75) (2 players)
Hero bets $3.5, UTG goes all-in for $20.50, Hero calls.

Showdown::
UTG shows .
UTG has : flush, king high.
Hero shows .
Hero has : straight, king high.

Final Pot
$2 is raked from a pot of $47.75.
UTG wins $45.75 with flush, king high.

yeah, the Q8 straight is way too vulnerable to slowplay. don't automatically get crazy w/ it (due to KQ obviously), but you need to make ppl pay on this flop, b/c they will call w/ a lot of 2nd best hands. bet it out or go for a nice checkraise.

you got full value on the turn, can't ask for more. at this point, his play screams a draw...

eventually you'll learn to fold that river quickly . a big raise like that on a board w/ a 4-card straight and 3 to a flush, you know he's got it...at most you're splitting w/ a Q, and you're very possibly losing to AQ in addition to the flush. it's not too bad of a call since it was about 2:1 and the flush was backdoor, but i think the possibility of AQ makes it enough to fold.

You have to protect this hand on the flop. Though this is tough luck. This river has to be a fold, what is he making a big reraise with that you beat??