Ok, while his his play on the flop was questionable, he probably decided a semibluff here would help make him money when he hit one of his 6 outs, and since he had so many checks in front of him this guy likely wasn't worried about losing $1.20 to a reraise or a diamond on the turn. So yea, he made a bad play here w/ negative ev, but where you went wrong was grossly overbetting the turn. UTG bet 90 cents and you raised him $9.90 cents, so when the BB raised you, you had trouble getting off your hand. Also, you made a bad call on the flop, because you shouldn't draw to a the ugly end of a straight draw in a really loose passive game like this, or draw to a straight with a flush draw present