6.Nf3 is a little conservative. Ndb5 is probably stronger, although really complicated and, as a practical matter for ann inexperienced player, it's probably a reasonable move. Nb3 is another reasonable move here, if you want to keep your f-pawn free for f2-f4.
7.Be3 however, is rather poor. Black has created a major weakness: the d5 square, and, by extension, the d6 pawn. These are major targets. You want to be able to land a piece on d5 and keep it there, so that you can exploit that weak square (and pressure the pawn behind it) throughout the entire game. To that end, Bg5! comes into play, with the idea of exchanging your bishop for his knight, for the purpose of weaking his grip on d5. (You trade off a piece which can never attack that square directly for a piece which can defend it.)
Similarly, 8.Bd3 seems like a poor move. Not only does the bishop do nothing here - being blocked by the pawn - but it's not helping you fight for d5 at all. Bc4! fights for the crucial square - and gives the Bishop some nice targets, too.
I really don't know what you were trying to do with Nd2. Prepare f4? Your pieces are now all jumbled up and getting in each other's way. Black siezes the opportunity to equalize by playign ...d5 - a direct function of your failure to control that square on your 7th and 8th moves.
The rest is really all basic tactics ... I'mnot crazy about b3, since healthy pawns should prove important in the endgame (your queenside pawn majority is only an asset if healthy) but I don't have time right now to go into more detail on the rest of the moves.
Me vs. the Sicilian
Linear Mode
