Hard Beat, But Avoidable?

[NotStudying]

I just got beat with a set of K's, where I had pocket KK and the third one on the board. The Enemy hit his straight on the turn, and I didn't see it. I'd like to think that I didn't see it because I was betting so aggressively that it was safe for me to conclude that no one would be drawing to the straight; I thought, perhaps that he had two pair or the fourth king. Anyway, it cost me my bankroll.

So was this my fault, or his? On the one hand, I lost; but on the other hand, even a blind hog finds an acorn every once in a while. Ignoring the fact that he won, was The Enemy wrong to call my bets before and after the flop? I'd appreciate any help on this. Here's the hand history:

Seat 1: Other Guy 1 ($16.35 in chips)
Seat 2: Our Hero ($12.90 in chips)
Seat 3: Other Guy 2 ($31.40 in chips)
Seat 4: Other Guy 3 ($14.85 in chips)
Seat 6: The Enemy ($15.10 in chips)
Other Guy 4: posts small blind $0.10
The Enemy: posts big blind $0.25
*** HOLE CARDS ***
Dealt to Our Hero [Kd Ks]
Other Guy 1: folds
Our Hero: raises $0.50 to $0.75
Other Guy 2: folds
Other Guy 3: calls $0.75
Other Guy 4: folds
The Enemy: calls $0.50
*** FLOP *** [6c 9d Kh]
The Enemy: checks
Our Hero: bets $0.25
Other Guy 3: raises $0.75 to $1
The Enemy: calls $1
Our Hero: raises $0.75 to $1.75
Other Guy 3: calls $0.75
The Enemy: calls $0.75
*** TURN *** [6c 9d Kh] [Th]
The Enemy: checks
Our Hero: bets $5
Other Guy 3: folds
The Enemy: raises $5 to $10
Our Hero: raises $0.40 to $10.40 and is all-in
The Enemy: calls $0.40
*** RIVER *** [6c 9d Kh Th] [4d]
*** SHOW DOWN ***
The Enemy: shows [Qh Jh] (a straight, Nine to King)
Our Hero: shows [Kd Ks] (three of a kind, Kings)
The Enemy collected $27 from pot
*** SUMMARY ***
Total pot $28.40 | Rake $1.40
Board [6c 9d Kh Th 4d]
Seat 1: Other Guy 1 folded before Flop (didn't bet)
Seat 2: Our Hero showed [Kd Ks] and lost with three of a kind, Kings
Seat 3: Other Guy 2 folded before Flop (didn't bet)
Seat 4: Other Guy 3 (button) folded on the Turn
Seat 5: Other Guy 4 (small blind) folded before Flop
Seat 6: The Enemy (big blind) showed [Qh Jh] and won ($27) with a straight, Nine to King