Thanks for the replies. I see now that I should have been able to defend my position better than in the actual game.
@EdLee: Unfortunatly I do not recall exactly how it went down. I was unsatisfied with my game and started to throw in stones ...that's not only bad for the game but also for your chances of remembering it

So I try to understand the basic pattern behind the situation in a local context.
I try to explain what baffled me again

This is how I learned it would go down:
http://www.lifein19x19.com/forum/download/file.php?id=1327
My opponent did not play that way but tried to trap my stone with a diagonal move (What are they called again?

).
I lost my nerve and lost somehow. At home I wanted to find out what happened and came basically across this:
http://www.lifein19x19.com/forum/download/file.php?id=1328
All sources end here ... as if it was self evident that white shouldn't play that way and as if it was completly clear what would happen now. It isn't 100% clear to me now, yet - but I feel I start to get it. I still can come up with too many variations to be satisfied, though.
For example:
This seems to lead to a Ko or allow white to stay connected and escape to the outside
http://www.lifein19x19.com/forum/download/file.php?id=1329
In conclusion: I'm confused and still looking for the best local result for white if both players continue to play as strong as possible

Jörg
PS: I now realise that the last position seems to be a catastrophy for white. It still gives a good impression of what I'm doing when I try to understand the position, though.