Misplaying (?) the Guicco Pianissimo; is 14. d4 correct? I recently lost an OTB game against a strong player (USCF) as white in the Guicco Pianissimo and have a few questions about it, especially 14. d4!?. Feedback/criticism are appreciated greatly.

Thanks everyone

[FEN ""]
[Event "Local Tournament"]
[Site "?"]
[Date "????.??.??"]
[Round "4"]
[White "Me"]
[Black "Opponent"]
[Result "0-1"]
[WhiteElo "1800"]
[BlackElo "2300"]
[ECO ""]

1.e4 e5 2.Nf3 Nc6 3.Bc4 Nf6 4.d3 { I generally enjoy playing these positions for white. } 4...Bc5 5.O-O d6 6.c3 a6 7.a4 Ba7 8.Nbd2 O-O 9.b4!? { Do I really have enough time to play this expansive move here? Perhaps it's better to continue by focusing on development. } ( 9.Bb3 { Followed by Nc4 and Be3 is probably the best way to get the dark-squared bishop into the game. } ) 9...Ne7 10.Bb3 Ng6 11.Nc4 b5! { With my pawn on b4, it seems like this advance blocks my position much more severely than it would otherwise. } 12.axb5 axb5 13.Ne3 { Here, I'm not entirely sure if e3 is the best square. } ( 13.Na5 { this move creates some queenside threats, but I'm worried that the knight will become out of play. } ) 13...Nf4 { A nice outpost, since I can't really play } 14.d4!? { Open the position straight away, or wait? I felt that I almost had no strategic ideas left besides playing this move, but perhaps I should attempt to improve my position beforehand. } ( 14.Qc2 Bb7 { I didn't like this method, because I felt paralyzed by the pressure on the e4 square. } ) ( 14.Re1 { Perhaps I should continue preparatory moves like Re1, Qc2/Qd2 and Bb2, anticipating the opening of the position. } ) 14...Qe8 ( 14...Nxe4 15.Qc2 { Doesn't work due to } 15...Nxc3! { So, how would I have actually been able to proceed after 14... Nxe4? } ) 15.dxe5? { I feel that relieving this tension is a mistake. Re1 looks interesting, keeping a lot of tactical ideas alive in the center. } ( 15.Re1 Nxe4 16.Qc2 Bb7 17.Nf5 { Looks like a respectable position. } ) ( 15.Nd5 N4xd5 16.Bxd5 Nxd5 17.exd5 { Also looks interesting, with black's misplaced queen and undeveloped c8-bishop. } ) 15...dxe5 16.Nd5?? { Now here I'm missing a tactic that I should not miss. Being exhausted isn't a perfect excuse, but I was quite physically exhausted during this game. At this point, I also realize that playing Bb2 far in advance would have eliminated these tactics on the a-file. } ( 16.Nd5 ) ( 16.Bb2 { Might still hold an equal battle } 16...Nxe4? 17.Bd5 Nxd5 18.Qxd5 { Forking } ) 16...N4xd5 17.exd5 Bxf2+! 18.Rxf2 Rxa1 19.Ra2 { I don't know what else I can do here besides try to trade the strong rook. } 19...Rxa2 20.Bxa2 Bg4 21.h3 Bh5 22.g4 Bg6 23.d6 cxd6 24.Qxd6 Qd8 ( 24...Qa8 { Makes things easier. } ) 25.Qxd8 Rxd8 26.Kf2 Ne4+ 27.Ke3 Nxc3 28.Bb3 Rd3+ { And the bishop falls. } ( 28...Rd3+ 29.Kf2 Ne4+ )  0-1
I haven't played the Italian game in some time, but my thoughts are in the replayer below:

[FEN ""]

  1. e4             e5            
  2. Nf3            Nc6           
  3. Bc4            Nf6           
  4. d3 {You said you like these kinds of positions. Given that the first game of yours I analysed started with 1.d4, it may be advisable to stick to a smaller opening repertoire, e.g. always starting with 1.e4. Either way, I think you played the opening fine}             Bc5           
  5. O-O {5.Be3 is common in the Italian game, hoping for 5...Bxe3 6.fxe3, strengthening the centre and giving an open file for the rook. But it is a bit double edged, as sometimes black can play Ng4}            d6            
  6. c3             a6            
  7. a4 {7.d4 is the key advance that you have prepared for, so I'm not sure why you didn't play it} (7.d4 exd4 8.cxd4 Bb6)            Ba7           
  8. Nbd2 {The queenside bishop and knight are the worse pieces in the game for you. If you had played 7.d4, then the c3 square may have been available for the knight and the bishop could come to e3 or g5}          O-O           
  9. b4             Ne7           
 10. Bb3 {It might be an unconventional square for the bishop in the Italian game, but you shouldn't be moving the same 2 pieces over-and-over again. I don't know what your Bb3 and Nc4 plans aimed to achieve} (10.Bb2)            Ng6           
 11. Nc4            b5            
 12. axb5           axb5          
 13. Ne3 {13.Ne3 isn't such a bad move, as long as either Bb2 or Nc2 are played to defend the a1 rook. 13.Na5 doesn't achieve much as the c6 square can't be occupied}           Nf4           
 14. d4             Qe8           
 15. dxe5           dxe5          
 16. Nd5            N4xd5         
 17. exd5           Bxf2+         
 18. Rxf2           Rxa1          
 19. Ra2            Rxa2          
 20. Bxa2           Bg4           
 21. h3             Bh5           
 22. g4             Bg6           
 23. d6 {This loses a pawn. I would try 23. Qe2} cxd6 (23...cxd6 24.Nh4 Qc6 25.Nxg6 hxg6 26.Bb2 Qe4 27.Bc1 Ra8 28.Bb3)           
 24. Qxd6 {This loses 2 pawns. Preferable is 24. Nh4} Qd8 (24...Qa8 25.Nxe5 Rd8 26.Qb6 Rd1+ 27.Kf2 Rxc1 28.Kg3 Rxc3+ 29.Kh4 Rc2 30.Nxg6 hxg6)
 25. Qxd8           Rxd8          
 26. Kf2 {I don't know why you advanced the king into check. I would have tried to activate the dark square bishop with 26.Bg5}           Ne4+          
 27. Ke3            Nxc3          
 28. Bb3            Rd3+          
 0-1


Summary


You didn't misplay the opening other than not playing the d4 break
I'm guessing that you have quite a wide repertoire seeing as you pay both 1.e4 and 1.d4. This is fine, but you may want to focus on just one
You moved the same pieces (queenside knight and light square bishop) rather than developing the dark square bishop
Towards the end there were multiple tactical blunders such as 26. Kf2, rather than 26. Bg5. The game would have still been tough, but those tactics partly stem from never developing the dark square bishop