A game where a shallow glance at the intentions of an opponent's moves exploded my winning advantage.

That's a very unusual approach by White: In general in the exchange variation White plays an early c3, reinforcing his d-pawn. I think 12,Bh6 was bad. Exactly how is he going to strengthen his attack on Black's King? Just a Queen and a Knight won't do it.

Wasn't 19...Bb5 very good for you? Also, I think 21..Rxc1 was better for you. If 22.Rxc1 Qxa3 or  22.Qxc1 Nxg4

It was a difficult game if you'd played 30...fxg5, but you're still breathing

c3 makes sense. A bit passive maybe, but it blunts the c-file. I don't know much about the Caro-Kann (or any opening, for that matter).

12. Bh6 was quite bad. Left his Queenside in tatters.

19 ...Bb5 does look great; I didn't even notice it. Seizes the initiative, and leaves White on the defensive (defusing whatever attacking hopes he had). Probably simplifying.

21 ...Rxc1 also makes more sense; moves like those are somwhat more difficult for me to see, still. I'm trying to get a feel for exchanges like that which gain time and allow for multiple variations.

Thanks for the sharp eye and comment!

Good eye. 21 Ng5 does look like it causes some troubles, and White will win at least a pawn, but 21 ...Qd2 22 Nxf7 Qxh6 23 Nxh6+ Kg7 looks to be just fine for Black.