Every loss is an opportunity to learn a lesson. That lesson is more likely to stick if you remember the pain you felt when you blundered.
I have a file in which I keep such lessons. After an OTB game in which I blundered, I print out the pre-blunder position, write down what I did wrong and what the lesson is and file it. I look at that file before I go and play my next game, to remember the pain and the lesson.
I find that my blunders seem to increase, I mean at one point I was winnig the game and i blundered to a stupid loss. He had Nf4 which he missed luckily, but i blundered.
How do I just get over it psychologically?
http://www.chess.com/livechess/game?id=1136354773