You mentioned comments about the opening, but the fate of the game swung back and forth several times in the late endgame.
After White 235, you passed:
- Click Here To Show Diagram Code
[go]$$Wcm1
$$ ---------------------------------------
$$ | . . O X X . . . X O . . . . O O X . . |
$$ | . . O O X . X . X O . . O . O X . X . |
$$ | . . . O X . . X O O O O . . O X . . . |
$$ | . . . O O X . X X X X X O O O O X X . |
$$ | . . O X X X X O O O X X X O X . . . . |
$$ | O O . O . . O . O X O O X X X X X . . |
$$ | X X O O X X O O O . O . O X X O X . . |
$$ | . X X O O O X X O . . O O O O O X . . |
$$ | . . X O . O O X W O X O X X X O X X . |
$$ | . . X X O O X X . O O X . O X X O X X |
$$ | . . . X X X . X O O X X . O . O O O X |
$$ | . . O . . . . O X O X X O . O . O O O |
$$ | . . . O X . O . X X O X O O O . O X X |
$$ | . . . O X X X X X O O O X X X O O X . |
$$ | . . X X O X O X X O . O X . O X O X . |
$$ | . . X O O O O O O O O X X . . X X . . |
$$ | . . . X X O O . . . O O X X X . . . . |
$$ | . . . X O . O . O . . O O X . . . . . |
$$ | . . . X O . . O . . . O X X . . . . . |
$$ ---------------------------------------[/go]
There are a few endgame moves left, so it's a bit early to pass, but most importantly, after you passed, white was able to kill the four stones in the lower left.
That capture cost you more than 8 points. Since the final score was White +7.5, losing those stones was a game-losing mistake. Let's take a minute to look at them.
Right now, white cannot cut:
- Click Here To Show Diagram Code
[go]$$Wcm1 White's cut fails
$$ ---------------------------------------
$$ | . . O X X . . . X O . . . . O O X . . |
$$ | . . O O X . X . X O . . O . O X . X . |
$$ | . . . O X . . X O O O O . . O X . . . |
$$ | . . . O O X . X X X X X O O O O X X . |
$$ | . . O X X X X O O O X X X O X . . . . |
$$ | O O . O . . O . O X O O X X X X X . . |
$$ | X X O O X X O O O . O . O X X O X . . |
$$ | . X X O O O X X O . . O O O O O X . . |
$$ | . . X O . O O X W O X O X X X O X X . |
$$ | . . X X O O X X . O O X . O X X O X X |
$$ | . . . X X X . X O O X X . O . O O O X |
$$ | . . O . . . . O X O X X O . O . O O O |
$$ | . . . O X . O . X X O X O O O . O X X |
$$ | . 7 . O X X X X X O O O X X X O O X . |
$$ | . 6 X X O X O X X O . O X . O X O X . |
$$ | 8 5 X O O O O O O O O X X . . X X . . |
$$ | . 3 1 X X O O . . . O O X X X . . . . |
$$ | . 4 2 X O . O . O . . O O X . . . . . |
$$ | . . . X O . . O . . . O X X . . . . . |
$$ ---------------------------------------[/go]
But notice that black's capturing group on the outside only wins the capturing race by one liberty. That means if those black stones lose a liberty, this sequence doesn't work for us anymore (foreshadowing).
After you pass, white plays to cut, and you block like so:
- Click Here To Show Diagram Code
[go]$$Wcm1 White has plans to cause trouble
$$ ---------------------------------------
$$ | . . O X X . . . X O . . . . O O X . . |
$$ | . . O O X . X . X O . . O . O X . X . |
$$ | . . . O X . . X O O O O . . O X . . . |
$$ | . . . O O X . X X X X X O O O O X X . |
$$ | . . O X X X X O O O X X X O X . . . . |
$$ | O O . O . . O . O X O O X X X X X . . |
$$ | X X O O X X O O O . O . O X X O X . . |
$$ | . X X O O O X X O . . O O O O O X . . |
$$ | . . X O . O O X O O X O X X X O X X . |
$$ | . . X X O O X X . O O X . O X X O X X |
$$ | . . . X X X . X O O X X . O . O O O X |
$$ | . . O 3 1 2 . O X O X X O . O . O O O |
$$ | . . . O X . O . X X O X O O O . O X X |
$$ | . . . O X X X X X O O O X X X O O X . |
$$ | . . X X O X O X X O . O X . O X O X . |
$$ | . . X O O O O O O O O X X . . X X . . |
$$ | . . . X X O O . . . O O X X X . . . . |
$$ | . . . X O . O . O . . O O X . . . . . |
$$ | . . . X O . . O . . . O X X . . . . . |
$$ ---------------------------------------[/go]
After white connects with

, black has to connect with

to prevent losing the large black group. So far your moves were forced. Then white plays this

:
- Click Here To Show Diagram Code
[go]$$Wcm1 Forced to connect?
$$ ---------------------------------------
$$ | . . O X X . . . X O . . . . O O X . . |
$$ | . . O O X . X . X O . . O . O X . X . |
$$ | . . . O X . . X O O O O . . O X . . . |
$$ | . . . O O X . X X X X X O O O O X X . |
$$ | . . O X X X X O O O X X X O X . . . . |
$$ | O O . O . . O . O X O O X X X X X . . |
$$ | X X O O X X O O O . O . O X X O X . . |
$$ | . X X O O O X X O . . O O O O O X . . |
$$ | . . X O . O O X O O X O X X X O X X . |
$$ | . . X X O O X X . O O X . O X X O X X |
$$ | . . . X X X a X O O X X . O . O O O X |
$$ | . . O O O X 5 O X O X X O . O . O O O |
$$ | . c . O X 4 O . X X O X O O O . O X X |
$$ | . . b O X X X X X O O O X X X O O X . |
$$ | . . X X O X O X X O . O X . O X O X . |
$$ | . . X O O O O O O O O X X . . X X . . |
$$ | . . . X X O O . . . O O X X X . . . . |
$$ | . . . X O . O . O . . O O X . . . . . |
$$ | . . . X O . . O . . . O X X . . . . . |
$$ ---------------------------------------[/go]
It looks like this move is threatening to cut off your stones, so you responded with

at "a". Actually the cut doesn't work. Do you see why? Black does have problems though, since your left side has been cut in half. Those splitting white stones could be a real problem for you. Instead of

at a, I think a move like b or c would look better, although I can't read out the whole thing.
- Click Here To Show Diagram Code
[go]$$Wcm1 White's attack continues
$$ ---------------------------------------
$$ | . . O X X . . . X O . . . . O O X . . |
$$ | . . O O X . X . X O . . O . O X . X . |
$$ | . . . O X . . X O O O O . . O X . . . |
$$ | . . . O O X . X X X X X O O O O X X . |
$$ | . . O X X X X O O O X X X O X . . . . |
$$ | O O . O . . O . O X O O X X X X X . . |
$$ | X X O O X X O O O . O . O X X O X . . |
$$ | . X X O O O X X O . . O O O O O X . . |
$$ | . . X O . O O X O O X O X X X O X X . |
$$ | . . X X O O X X . O O X . O X X O X X |
$$ | . . . X X X X X O O X X . O . O O O X |
$$ | . . O O O X O O X O X X O . O . O O O |
$$ | . . . O X X O . X X O X O O O . O X X |
$$ | . . 7 O X X X X X O O O X X X O O X . |
$$ | . . X X O X O X X O . O X . O X O X . |
$$ | . . X O O O O O O O O X X . . X X . . |
$$ | . . . X X O O . . . O O X X X . . . . |
$$ | . . . X O . O . O . . O O X . . . . . |
$$ | . . . X O . . O . . . O X X . . . . . |
$$ ---------------------------------------[/go]
Now white plays 7. This is a scary play for black, because of that shortage of liberties earlier. Watch what happens now:
- Click Here To Show Diagram Code
[go]$$Wcm1 One liberty is enough
$$ ---------------------------------------
$$ | . . O X X . . . X O . . . . O O X . . |
$$ | . . O O X . X . X O . . O . O X . X . |
$$ | . . . O X . . X O O O O . . O X . . . |
$$ | . . . O O X . X X X X X O O O O X X . |
$$ | . . O X X X X O O O X X X O X . . . . |
$$ | O O . O . . O . O X O O X X X X X . . |
$$ | X X O O X X O O O . O . O X X O X . . |
$$ | . X X O O O X X O . . O O O O O X . . |
$$ | . . X O . O O X O O X O X X X O X X . |
$$ | . . X X O O X X . O O X . O X X O X X |
$$ | . . . X X X X X O O X X . O . O O O X |
$$ | . . O O O X O O X O X X O . O . O O O |
$$ | . . . O X X O . X X O X O O O . O X X |
$$ | . 7 O O X X X X X O O O X X X O O X . |
$$ | . 6 X X O X O X X O . O X . O X O X . |
$$ | . 5 X O O O O O O O O X X . . X X . . |
$$ | . 3 1 X X O O . . . O O X X X . . . . |
$$ | . 4 2 X O . O . O . . O O X . . . . . |
$$ | . . . X O . . O . . . O X X . . . . . |
$$ ---------------------------------------[/go]
I'm not sure exactly the best way to prevent this, maybe a sequence like this:
- Click Here To Show Diagram Code
[go]$$Wcm1 Stopping the cut
$$ ---------------------------------------
$$ | . . O X X . . . X O . . . . O O X . . |
$$ | . . O O X . X . X O . . O . O X . X . |
$$ | . . . O X . . X O O O O . . O X . . . |
$$ | . . . O O X . X X X X X O O O O X X . |
$$ | . . O X X X X O O O X X X O X . . . . |
$$ | O O . O . . O . O X O O X X X X X . . |
$$ | X X O O X X O O O . O . O X X O X . . |
$$ | . X X O O O X X O . . O O O O O X . . |
$$ | . . X O . O O X O O X O X X X O X X . |
$$ | . . X X O O X X . O O X . O X X O X X |
$$ | . . . X X X X X O O X X . O . O O O X |
$$ | . . O O O X O O X O X X O . O . O O O |
$$ | . . . O X X O . X X O X O O O . O X X |
$$ | . 9 7 O X X X X X O O O X X X O O X . |
$$ | . 8 X X O X O X X O . O X . O X O X . |
$$ | . . X O O O O O O O O X X . . X X . . |
$$ | . 0 . X X O O . . . O O X X X . . . . |
$$ | . . . X O . O . O . . O O X . . . . . |
$$ | . . . X O . . O . . . O X X . . . . . |
$$ ---------------------------------------[/go]
If you're not careful white can still cause trouble here, but I think black should be able to kill the white stones, since both sides are independently alive. (Don't take my word for it!)
As it went in the game, you blocked on the other side with

, and white ends up capturing the four stones and also getting a ko to live, which luckily for you black was able to win.
The pass, the unnessary block at

, and the wrong approach at

means you had 3 chances to save those stones and win the game. As Bill says, endgame is about fighting strength.