I believe I had control of this game and after reviewing it I believe that the mistake was in 18.c3...f5, I should have played ...Bb6, do you agree? Could you tell me what you think of it, or where could I have done better? thanks a lot. Oh by the way I play black.

 

 

 

 

 

 

 

I'll appreciate all your comments, thanks.  

5. ... b6. Your light square bishop already has a nice diagonal to come out on.

 

10. ... b5.  You are shutting in your bishop. This is like playing a piece down. 

 

11. ... Nb6. Where does the knight have to go from b6? 

 

18. ... f5. Yes, this is a mistake. You expose your king to a lot of danger. You don't have the defensive resources on that side of the board because your light squared bishop is stuck on a6. 

castling on your kingside while there was too much pressure was the problem in my opinion. He also has more active pieces than you after exchanging pawns on move 15. d5

well thanks a lot for your comments, I'll review the game once more and then get back at you.

18...f5 must be replaced with 18...Bb6. In the game, White had 20.dxe4.

bastiaan wrote: castling on your kingside while there was too much pressure was the problem in my opinion. He also has more active pieces than you after exchanging pawns on move 15. d5

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I agree....While you had lots of space on the queenside your pieces weren't really doing anything active at move 12.  After you castle I think white even missed a more appropriate reply with n-f5.  With possible sacks coming and just a superior position