I know how you feel. I can relate. I choose to see it differently, though...
If you saw moves that your opponent did not, it likely means that you are a better player than that person. Therefore, you deserve to win the game.
It doesn't always mean you're better, but for that series of moves, you certainly played better - seems like a paradox, but your opponent would have seen the crushing move if he had been playing better at that moment.
All in all, chess is a game where capitalizing on mistakes is key to victory. In GM games, the mistakes are more subtle (creating a weak square, or not putting a piece on it's best post, for instance), but mistakes are a part of chess.
If nobody ever made mistakes playing the game, we'd all draw each other all the time and there would be no point in playing!
Twice in the last day, just after hitting submit, I saw an incredible move for my opponents (a real Queen winning !!) attack in the one instance, and a wonderful attack on my King that would've just cleaned me up. Both of my opponents missed these moves, and when I returned to the game seeing that they hadn't played the move I was incredibly relieved, gaining a new lease on life.
The thing is, while I really like these games for other reasons, I've been doing my damndest to play technically correct, or optimal.
I feel like these horrible blunders are like blemishes on what I want to be little (alberit patzerish) works of art.
It's like the value of the game (if I win) is tarnished, because I'll always know that if my opponent saw that single move, I would've been entirely blown away...
It puts me in a weird feeling about the game - I mean, of course in all games of chess both sides make mistakes, and it's okay if you win due to your opponent making a few subpar moves that you're able to incrementally capitalize on; but this is like them missing a mate in 1.
I guess I should be happy that they missed it, but gosh... I feel like I "lost" the personal chess battle with myself.
Maybe after the game is finished I'll post the position as a puzzle...