and I still lost... How could I have grabbed a win out of this game?

To avoid complications black chould of played 19...Bg5, followed by f5,e4. He is better in game continuation too, although maybe hang on with 25Qh5ch ,followed by c3

7. f4 is hugely better.  You cost yourself a huge tempo and positional loss by removing your Knight from its active post.  Play continues 7 ... Be7 8. Be2 O-O 9. Qd2

8. Bc4 is strongest, Be2 is still probably better than the text.

10. Qd2 finishes development.

12. Re1 is stronger, preparing e5.

14. Qe2 prepares e5, the text move drops a pawn and creates an unfavorable trade series

31. Kf1 is better

34. f3 is stronger, the Queenside is irrelevant currently. The King needs to undermine the advance pawns or else...

When your opponent has connected passed pawns, trading one's rook loses the game as you see.