Breaking the tension

Please help me understand where I could do better during this game.
For all I know, 31.Re4 started the series of blunders for me (not that there wasn't any before).
During the entire game I was feeling the tension, but I can't spot even now all the chances that I missed to turn that into my favour.
Any feedback is more that welcome.

One of the more helpful positional things to tell you is probably this

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This sort of pawn structure can happen from many different openings, and when it does, it's really bad for black to have the knights like this. (The d7 knight is stifled by its own pawns and knight on f6. The natural squares to aim for are b5 and f5 because that's where black's pawn breaks are... but it's extremely difficult for this knight to influence those squares, so it's usually permanently passive)

Well, ok, with so many locked pawns it tends to be a maneuvering game, so it's not as if black will immediately lose. White has to show some technique, but objectively it's just bad, like, 99% of the time (doesn't matter which opening produces it).

Anyway, on to the game.

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So this was a bit aggressive from you, but your basic idea isn't bad. If black reacts by capturing your b5 pawn, then you open the c file with a gain of time (your rook is uncovered and attacks black's queen) and you have a lot of space on the queenside you can worth with.

Instead of that, if black pushes the pawn to c5, then we get the "bad" structure I warned about above (black plays c5, you can respond with d5).

Instead of capturing your b pawn or pushing c5, black can capture on d4, but anyway, one basic strategy for white is to build up pressure on the pawns like this, and try to force your opponent to either push a pawn or capture even though those options are less than favorable.

For that reason I'd say your next move was inconsistent (13.bxc). You spend 3 moves to trade b pawns... why? It was just a waste. The point of b5 should be to compel black to initiate a trade in some way (or you build up pressure to the point you can win material somewhere).

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Other than that, move 18.Bg5 was very bad, offering to trade your "good" bishop for black's "bad" bishop. (A good bishop is one whose friendly center pawns are on the opposite color, a bad bishop has friendly pawns on the same color. It's "bad" because it's blocked by its own pawns).

In similar situations black usually has to work very hard to trade off the dark square bishop. Offering to do it for black, and by giving up your good bishop, makes no sense.

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Black's move 15...c5 is bad (see first diagram).

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As for 32.Rxd4, that move was ok.

The problem was 34...Qa1 attacked your rook and you didn't notice. So you didn't save your rook. Black noticed and won your rook on move 35.

Hmm, the 2nd half of the post seems to just be telling you what not to do without offering any guidance on what to do.

So ok, after 15...c5 your very general goal is to play on the queenside (your furthest advanced center pawn is on the queenside, so you have a natural space advantage there).

So how do you "play" on the queenside? Again very generally, the goal is to come into contact with weak pawns. Black's a7 and d6 pawn can't be defended by a pawn, so they're good targets.

Ok, so how do you come into contact? Again very generally, first just try to infiltrate i.e. try to post some pieces on black's half of the board on the queenside. Squares like a5, b5, or b7. So first you might double rooks on the b file (for example).

Now during a real game there are lots of things to consider. For example black's move 17...Nh5 is trying to come to f4. So maybe you spend a move to stop that by playing g3. Or maybe you're about to infiltrate but it's prevented by a tactic so you have to calculate a lot... but mobilizing on the queenside, infiltrating, and coming into contact with weak pawns is the general strategic outline.

@llama47, thank you for such a detailed response. That really gave me something to think about.
Pawn structure is my terra incognita, but even with that the ideas of week pawns that I could target did not occur to me during the game. This is something I should pay more attention to.

The idea of my good bishop vs his bad bishop did not come to me either. I should have noticed how the pawns are positioned, but at that moment I just thought that bishop was one of my weakest pieces, because it was literally standing there and not doing anything.

And that goes very well with the advice to operate on the queen side. Once you said that, I see that after 17...Kh5 I started to change between the sides without doing anything on any of them.

Thanks for pointing to me so many aspects I totally missed.

You came out of the opening with a winning advantage.

18 Bg5?? is a blunder. 18...Bxg5 19 Nxg5 Nf4 is good for black as he trades his bad bishop Be7 on the color of his pawns for your good bishop Bd2 not on the color of your pawns and black gets an active knight at f4 as well. You had to deny him square f4 with 18 g3 and still hold a winning advantage.

33 Qxf3?? Qa1+ loses a rook. You had to defend 33 Kf1.

35 Kh3?? blunders a rook and loses the game, you had to save the rook 35 Rh4

@tygxc thanks a lot for the response!
18 Bg5?? was with the idea of 18...Bxg5 and my queen is threatening his knight, while my knight on that spot also creates checkmate tension.
Of course, now I see that I totally missed that knight on f4 would prevent my queen to go anywhere near that line.

Jeremy Silman's Reassess your chess book is great for learning in more detail principles behind concepts like good vs bad bishop:  https://www.amazon.com/dp/B00M9WCX7A/

llama74 already did a great analysis.  The only thing I'd add is more about black's Qa1 move.  That could have happened after your queen abandoned the back rank:  33. Qxf3??

Look for possible ways your opponent can check you.  Look for possible moves that can happen once they have tempo with a check.

Black is threatening Re1+ here, winning the queen/rook exchange.  You need to protect the e1 square.  It's not always intuitive to move your king toward danger, but you need to guard e1 twice.

After your opponent moves, ask yourself why he did that. What new threat does black have after Re8 that he didn't have previously?

32. Rxd4? isn't a good move.  Black just immobilized your rook and gained control of the e file for a measly pawn.  Re6 would have been much better.  Depending on what's going on, you could leave your rook there no matter what.  Suppose black maneuvers his knight to a position to threaten your rook.  fxe6 gives you a very solid passed pawn.  I'd argue a pawn on e6 plus black's knight is worth more than your rook.