It was bound to happen eventually. I was doing far too well for far too long not to get overcomfortable.

Besides missing the obvious, I fiddled on the queensice for too long without any real gain, and perhaps should have traded queens when there was a chance.

I remember playing 7Na3 in a OTB match once. One of high board first team, didn't turn up, and i was thrown in 1/2 hour into session. Rushed my opening to try catch up, then looked in horror when noticed 6...d6 hadn't been played :). Of course, black should have very good position, after silly 7.Na3 think opponent played 7...Bb4 and then prepared d5. Think 7...BxN is kindly removing a bad peice and giving two bishops.

I know, but the ruined pawn structure on the queenside would compensate for it. Or so I thought at the time.

That's true but point is that once black get's d5 in after 7Bb4, white has no compensation at all for Na3. After 7...BxN, white has some good aspects of his position, the two bishops and something to play for. Black position still playable after 7...BXN of course, but think 7.Bb4 gives bigger advantage basically.

13. Bd5 struck me as a mistake.  I would have played 13. Bb2 and then Nd5.  Then white must avoid moves that can be punished by a fork on b6, c7, or e7!  For black it both makes development diffucult, and moving the queen nervewracking.  It would have been such a good place for your knight I would consider the position about equal!

Of course black trying to snap off the bishop with Nd4 Nxb3 would be no concern as it fixes your pawn structure, and again gives the queen something to be nervous about.

I was black

Isn't 7.Nd6+ supposed to be better for White here?

8... Qa5 drops a pawn

You didn't read me correctly, I think.

You didn't play the normal 6...d6, which is meant to prevent 7.Nd6+ Bxd6 8.Qxd6. So White should have played that.

No, I read you fine. Nd6+ Bxd6 Qxd6 Qa5 Bd2 (Qd2) Qb4 drops the e pawn or weakens the kingside by forcing f3

I think I'd play 8...Qa5 9.Bd2 Qb4 10.Qxb4 Nxb4 11.0-0-0, or 9.Bd3. Both must be better for White than 7.Na3?!...

Yes I think so too, and 8...Qe7 is more common than 8...Qa5