What has gone wrong?

I'd like to make a quick post about a game that is a great example of how my play has gone downhill the past few days. I'm trying to learn the Philidor defense because it can be very solid if played correctly. In this game I really outplayed my opponent in the opening, and (almost) every move was a good, sound developing move with a threat. Then I just didn't think correctly about an exchange, thinking I would go a piece up, and my advantage completely dissipated. I didn't feel like making all the diagrams for this post, so I came up with a new idea. You can copy what's below and paste it into BabasChess or some other PGN viewer and read the post as comments after the moves. Pretty cool huh!?! [Event "rated blitz match"] [Site "Free Internet Chess Server"] [Date "2009.01.28"] [White "----"] [Black "waparker"] [Result "1-0"] [WhiteElo "1097"] [BlackElo "1142"] [ECO "B00"] [TimeControl "120+12"] 1. e4 d6 {This is how alot of GMs do the move order for the Philidor defense. It looks like the dynamic Pirc defense for a little while and then transposes.} 2. Bc4 Nf6 {I have to watch out for a quick attack on f7.} 3. Nc3 e5 {Nc3 gave me time to develop without worrying as much about f7. Better for white is probably Nf3.} 4. Qf3 c6 {Qf3 threatens to try to dislodge the knight with 5. Nd5. The knight is pinned to the mate on f7, so I would have to double my pawns if I allowed Nd5. That is why I played c6.} 5. h3 Be7 {He wants to keep my bishop off of g4. h3 wastes time, better is probably d4, or developing the King's knight. Be7 clearing the way for castling.} 6. Nge2 O-O 7. d4 exd4 {My first inaccuracy. I wanted to have e5 as a square for the knight to chase away the queen. However, the knight is two moves away from e5, so capturing does nothing for me, it only gives away my advanced central pawn. I should have played 7... Nbd7.} 8. Nxd4 Nbd7 9. O-O Ne5 {Luckily for me, I still got Ne5 in.} 10. Qe2 b5 {I have read that it is important in the Philidor for white to prevent ...b5 by playing a4. I am gaining time on the bishop and eyeing the skewering line between the Queen on e2 and the rook on f1.} 11. Bb3 a5 12. a4 b4! {Gaining another tempo on white's minor piece! The skewer should come next move.} 13. Nd1 Qd7? {Completely illogical move. I have just enough time here at move 13 to play Ba6 winning the exchange. The white light-square bishop can't block because my e5-knight covers the c4 square. Unfortunately, I just didn't see that my lovely knight on e5 also covers the c6 square so I don't have to worry about 14. Nxc6.} 14. Nf3 Ba6 {White's Nf3 takes all the bite out of Ba6.} 15. Nxe5 Bxe2 {Here is where I miscalculated. I thought I would be going up a piece here. It ends up that I lose alot of time getting my bishop out of the morass so my advantage in time is gone, and I have less central space. Actually my time advantage was probably gone after 13 ... Qd7} 16. Nxd7 Nxd7 17. Re1 Ba6 18. Ne3 Nc5 19. Bc4 Nxe4?? {I knew in the back of my mind that I was losing a piece by making this move, but I made it anyway. This has been the hallmark of my crappy play as of late. The discovered double attack is just too obvious, but I missed it. I would still have a playable game with 19... Bf6 or ....Bxc4.} 20. Bxa6 Rxa6 21. Nf5 Bf6 {waparker resigns} 1-0