Those of us who are total depressives (I'm the president, chairman of the board, and world champion) have a tendency to do three things, and you just did all of them. We catastrophize (this bad thing that happened is a calamity; it's all over!); we personalize (It's all my fault!); and we do a third thing I can't make a verb out of, but it has to do with permanence (Things will never get better!) Take a deep breath, go read this:
http://www.mastersforum.com/archives/seligman/selig.htmthen when you have more time, read his book "Learned Optimism"
http://www.amazon.com/exec/obidos/ASIN/0671019112/thewhythingsdont/102-2835326-4505706but in the mean time, remember the following:
Sometimes it's hard to do what you know is the right thing.
Everybody makes mistakes.
Making one mistake isn't the end of the world, doesn't make you a bad person, and isn't going to ruin your life.
Men are weasel-bastard-shitboxes, and are to be avoided. (Ok, I'm mostly kidding about that one.)
The sun is probably going to rise in the morning.
You never lose what you've been working toward. Two steps forward and one step back is the normal way humans progress toward personal growth.
Now
you smile!