By heart I am a d4 player and I like maneuvering games especially ones in the Ruy from white.
Simul analysis from my view.
Move 9: We have a so called Berlin Endgame
Whites long term plan is to get rid of the two bishops and claim a better position. Since black cannot castle white wants to prevent black from developing and push his kingside majority.
Black wants to push the queenside majority and get rid of the doubled pawns. Often times black will want to play Kb6 to keep his king in safety since white does not have a light squared bishop or queen to attack the light square of b6.
Move 10:
Black: Played b6 intending to walk the king over to the queens side to activate the A1 rook.
I had never seen the move Bf4 so I did not see whites long term plan but I figured it focused on the central e5 pawn.
Move 12: Rad1 I was figuring this move would be played to stop my king from moving away from the bishop and in some cases threatening the bishop with a pawn sac followed by knight to e5.
Black: Moved king out of the pin to avoid the potential isolated pawn or pawn sac however uncommon it could be an issue with my playstyle.
Move 13: Ne4. I was a bit confused to where the knight would be going and felt it might be out of play if I disturbed it from its nice central square. After playing Bc6 I regretted the plan afterwards as I seen the knight really is not doing much even on the nice central square. Since it would have to move anyway to find a better home I might as well not attack it and make it go to a better spot.
Move 15: I predicted the knight was heading to either d5 or b5. And I was almost thinking b5 was better because you still put pressure on my c7 pawn but also potentially aiming at a7 if my rook moves away. After the game I discounted the b5 move as I can just push and make it go back so d5 was the better square.
Here is where I made a plan but it turned out to be a bit slow. My plan was to play g5 and kick the bishop away thinking it might want to stay on the c1-h6 diagonal. Then play Ng6 and Bg7 attacking e5. Since I could easily put pressure on e5 and it seems a bit slow to move the knight away to push f4. I had dreams but quite ones of winning the e5 pawn. Since I could immediately build up on the e5 square with the bishop knight and rook as well as starting the plan with tempo I did not think it was a bad move until the next few moves happened.
Move 17. I did not see or think about the move e6 and that just stopped my plans of winning it. I was in no way going to take it giving myself isolated pawn and you would pick up the c7 pawn while attacking my rook. Then picking up the isolated e6 pawn.
I had to abort and take the knight. I lost time here having to move my bishop and felt retreating it to stop Exf7 with the potential threat of Re8 or Rd8 at some point queening.
Move 20. I pretty much felt like I had to take to stop queening and my plans were pretty much all over. I could not come up with something else except to start pushing my queen side majority hoping for an advantage there. But since black has worse activity it feels doomed from 21 onward. I had thought about the knight being rerouted to f5 but discounted it as the threat since I have Rf8 and totally missed that the knight was going to d5 instead.