Thanks for your kind words, you are right about 18. ... Nf5. In retrospect 18. ... Qf5 would have been better, because after 19.Qxf5 Nxf5, the knight is now somewhat better on f5 due to the missing threat of Bg5.
And you are right about 32. ... g5, but i was already losing there in my opinion.
I think the 35.Nd2 line can be repaired with 35. ... Be5 36.Ne4 h6. But well, he didn't play it anyway 
Thanks again for your help.
Hello forum,
i recently annotated one of my losses and i am still unsure about what exactly went wrong. If anybody is willing to help it is highly appreciated.
http://blog.chess.com/sirprim/losing-big-time
Thanks,
sirprim
P.S.: The opening was (almost) a Scotch Four Knights, maybe someone knows his way around there.