wow, how I lost this game?

At move 26 I thought I had a winning position:

Move 26

Then came the disaster. I guess that's the difference between a 1700 and a 2000 in rating ;)

So, please tell me, what were my first mistake from then on?

Thank you! :)

mistake

oh, very interesting move 42. Thanks a lot.

What if you had done 42. C9 instead?

also good

wow, I analyzed c9, but the line wasn't sucessful. I didn't spot that move 48, of course.

Oh my!! xD

Can't believe I made so many mistakes during the whole game :O
Looks like I basically won by luck...