Made my Flush, don't feel so good. 3/6 PS

[Osprey]

How's my line in this hand?

Villain recently sat down, I don't have a read.
PokerStars 3/6 Hold'em (10 handed) FTR converter on zerodivide.cx

Preflop: Hero is SB with Qh, 8h.
5 folds, MP3 (Cthulhu) calls, 2 folds, Hero completes, BB checks.

Flop: (3 SB) Th, 5s, 6h (3 players)
Hero bets, BB raises, Cthulhu calls, Hero calls.

Turn: (4.50 BB) 7h (3 players)
Hero checks, BB bets, Cthulhu raises, Hero 3-bets, BB calls, Cthulhu caps, Hero calls, BB calls.

River: (16.50 BB) 3c (3 players)
Hero checks, BB checks, Cthulhu bets, Hero calls, BB folds.

Final Pot: 18.50 BB