Englund Gambit Complex

"6. fxe5 free pawn." If you think you're a pawn up here this is a bad evaluation. Both of your e-pawns are weak since they are isolated. Notice that 7. Bf4 you are using the power of a whole piece just to hold on to your pawn.
8. Nc3. I think you either don't see it coming or you underestimat the damage that can be done by Bb4 and Bxc3 giving you a weak a pawn and two weak c-pawns. This game is about pawn structure and yours is getting worse and worse.
9. 0-0-0 I may have just bit the bullet here, admit that the e5 pawn is not worth protecting and play Bd2 in order to secure the queenside pawn structure.
27. Bc5. This doesn't really accomplish anything. 27. Re4 wins the c4 pawn (If Ng6 Rxc4 Nxe5 Re4 picks up the e6 pawn, black still has an advantage because your doubled c-pawns aren't worth much more than 1 pawn).
How about 35. Be5. You threaten to take the knight because the g7 pawn is pinned. If the 35. ... Ne8 protecting g7 then you have 36. Re7 winning the e6 pawn. If 35. ... Kh8 then 36. Bxf6 gxf6 Rxf6 and if 35. ... Kg8 then 36. Re7 and now white can't play Nxg4 because of Rxg7 winning the knight.

Blocking the f-pawn with your knight on move 3 is not a problem for a couple reasons. The first reason is king safety: if you castle kingside, you want your f pawn on the second rank for some time to come. The second reason is that the f-pawn doesn't do a good job protecting the e5 pawn... because if it ever takes back on e5, you now have two isolated (doubled) pawns on the e file.
You discovered both reasons during the game. You no longer wanted to castle kingside because of the moved f pawn, and you played fxe giving you two isolated (doubled) pawns.
I would suggest on move 3 defending with the knight as you had also considered. Keep the e5 pawn defended from capture by black's pieces. Eventually he will want to attack with a pawn or even just to move the pawn forward on the d file to open up his bishop to move. At that point you could play exd. You already got to capture once with this pawn before, so you are a pawn to the good.
Beginners and even intermediates are told to play openings that tend to open games because the open game will be more likely to tax your tactical computation and more immediately punish errors, tactical or strategic. This makes it easier to see what went wrong and improve your game. The goal (when intermediate players are told to play open games) is not to have them win more but to have them learn more.