Where did I go wrong? QGD loss as black [fen ""]    
[Date "6/8/2018"]
[White "Anonymous"]
[Black "Me"]
[Result "1-0"]
[WhiteElo "2146"]
[BlackElo "1874"]
[Opening "Semi-Slav Defense"]

1. d4 d5 2. c4 c6 3. Nf3 Nf6 4. Nc3 e6 5. cxd5 exd5 6. Bg5 Be7 7. Qc2 h6 8. Bf4 O-O 9. e3 Nbd7 10. Bd3 Re8 11. O-O Nf8 12. a3 Ne6 13. Bg3 Bd7 14. Ne5 Bf8 15. Bh4 Be7 16. Bg3 Nf8 17. b4 a6 18. Na4 Nh5 19. Rab1 Nxg3 20. hxg3 Bf6 21. Nf3 Ne6 22. Nc5 Qc7 23. Rfc1 Ng5 24. a4 Nxf3+ 25. gxf3 g6 26. b5 axb5 27. axb5 Rab8 28. Nxd7 Qxd7 29. bxc6 bxc6 30. Rxb8 Rxb8 31. Qxc6 Qxc6 32. Rxc6 Be7 33. Rc7 Kf8 34. Ba6 Rb1+ 35. Kg2 Bd6 36. Rb7 Ra1 37. Bb5 Rc1 38. Rd7 Rb1 39. Bc6 Be7 40. Bxd5 Rb6 41. Ra7 h5 42. Ba2 f5 43. Bc4 Rc6 44. Bd5 Rd6 45. Ba2 h4 46. gxh4 Bxh4 47. Bc4 Rc6 48. Rf7+ Ke8 49. Rh7 Rxc4 50. Rxh4 Ke7 51. Rh7+ Ke6 52. Rb7 Rc6 53. Rb5 Rd6 54. Kg3 g5 55. Rb1 Kf6 56. Rb5 Ke6 57. f4 g4 58. Re5+ Kf6 59. f3 gxf3 60. Kxf3 Ra6 61. Ke2 Ra2+ 62. Kd3 Ra4 63. d5 Ra6 64. Kc4 Rd6 65. Kc5 Ra6 66. Re6+ Rxe6 67. dxe6 Kxe6 68. Kc6 1-0


My rating: 1874

My opponent's rating: 2149

Feel free to address these points or any other important bits of analysis throughout the game:


I've saw some recommendations after the game of 6...h6 7.Bh4 Bf5.
Perhaps I should play 7...O-O and Nbd7 straight away without 7...h6?
12...Ne6?! seems like it gave me some problems. Nxf7 followed by Bg6 can now be considered. What else should I be doing? Perhaps 12...a5 was better? How about 12...Bd6?
Is 14...Bf8 a waste? I wanted to open the e-file and was struggling to find a productive move.
16...Nf8: I felt that my knight was misplaced due to the concerns with white taking on f7.
Perhaps instead of 17...a6, I should be advancing on the kingside as quick as possible. Is this good thinking?
Maybe 21...h5 instead of putting the knight back on e6?
Was 27...Bc8 more stubborn? I think white could still seize control of the a-file.
After move 32, I felt that I was lost. The d5-pawn can't be held onto forever. Maybe an opposite colored bishops ending with 2 extra pawns would've been a bit more unclear than the rook ending? But I felt it was still quite winning for white.


Thanks!
I'll go through the game and address your points.


In the opening, you should have played 6...Bf5 (or 6...h6 then 7...Bf5, like you said). The reason for this is that in the Exchange QGD, your light-squared bishop is bad, while White's light-squared bishop is good. If White loses his light-squared bishop, playing the thematic b5 push of the minority attack becomes difficult. Back to the point: by developing your bishop to f5, White cannot bring his bishop to d3, or else you do the favorable exchange.
7...h6 is a very subtle mistake, for a few reasons. First, in the exchange QGD White would prefer to have his bishop on f4, not g5. The reason he doesn't play 6.Bf4 immediately is that you can answer with 6...Bd6! in one go. By playing 7...h6, you give White a "second chance" to play Bf4, and now you have to waste another move to counter with ...Bd6. The second reason 7...h6 is a mistake is that you can't play ...Ng6 in the middlegame, since the knight is not supported enough on g6 and White can just played Bxg6. In the Exchange QGD, playing ...Ng6 is very important. It's far better than ...Ne6, since it blocks White's Qc2+Bd3 battery, and also attacks White's dark-squared bishop on h4 or f4.
12...Ne6 is actually fine, given your options. After 13.Bd3, you should have played 13...g6, 14...Ng7, 15...Bf5. This is an important idea that lets you exchange light-squared bishops. Remember it, if you are only able to develop your f8-knight to e6 (normally, prefer the g6-square for the knight).
14...Bf8 is normally a good idea, but because White has 15.Bh4 it's not so good here. A better plan would be playing 14...Rc8 and 15...c5. This undermines the e5-knight's support from the d4-pawn, and exploits the White queen's position on c2.
I don't think 16...Nf8 is that bad a move, given that you wanted to play ...Nh5. Playing ...Nh5 immediately would have dropped the knight due to Nxf7 Kxf7 Bg6+.
17...a6 was absolutely fine. By playing ...a6, you force White to waste at least a tempo playing a4 (since without this move he can't play b5 now, due to ...a6). Also, if White wants to play a4 then he must protect the b4-pawn, or else you'll play ...Bxb4. So ...a6 really ends up forcing White to waste about two tempi countering it.
I like 21...h5! After playing ...h4 and exchanging everything, you end up with a queen on h4. Then, you can do a Rook lift with ...Re6 + ...Rh6, building a battery on the h-file. Another idea is even playing 21...g5!? followed by ...g4, forcing White's knight to move away, and then ...h5 and ...h4. The problem is that White can play 22.Bf5, but you can still play 22...g4 with an interesting game.
I don't like 27...Bc8 because it breaks the coordination of your Rooks. After 28.bxc6 bxc6 29.Ra1, you're facing a difficult defence. Backing up two moves, I think 25...Re7 is strong, simply protecting the d7-bishop. After 26.b5 cxb5! 27.axb5 Bxb5 28.Bxb5 axb5 29.Rxb5, your e7-rook and queen protect the b7-pawn (which is passed, to boot). Note that on 27.Nxd7 Qxd7 28.axb5, you can play 28...a5! with a dangerous passed a-pawn. This trick of side-stepping White's b5-push with ...a5 is how Karpov once tricked Korchnoi in a game.
You're right, the endgame was lost. The d5-pawn was too weak to be held on to, and then White's just up two pawns. An opposite-coloured bishop ending without rooks wouldn't have helped much. Opposite-coloured bishops are only good against two extra pawns if you can set up a blockade on the colour complex of your bishops. With all White's pawns so close together, they form a veritable armada that can keep control over the dark squares.