The most painful defeat of my life...

BTW I changed my profile picture and name to avoid prep

dang.

Don't worry about losing 2000, though. I lost to a 1500 when all four opponents were rated below 1800, and i only lost 20 points (2044->2029)

I feel like you could have held the game up until the last blunder. Maybe it's a mentality thing. But what I do when I get in worse positions is remind myself that

(1) I've been in worse, and not lost

(2) How satisfying it would be if I didn't lose and

(3) Finding a continuation to defend and try to equalize is just as fun as trying to push for an advantage.

A painful chess loss is unlike anything else in life. I'm always shocked by how hard some of my losses have affected me. I've had some OTB tournament losses that have been terribly painful. Feel depressed, can't sleep, spend too much time dwelling on what should have been. It's crazy. In all other areas of my life I'm optimistic and can stay positive in just about every situation, but not when it comes to some of my harsh OTB chess losses. I've had some losses that still cause me frustration and resentment even years later. Chess is weird.  

We've all had those days. Keep focus, don't lose heart and reassure yourself that this is going to be just another spot on the sun. The most important thing to do to analyze the game (which you've already done so brilliantly) and note down where you went wrong ("Do I lose focus and relax easily in winning positions?"). Engrave the general improvements in your mind, and stop it at that. This game is done, you've learned from it, so it's time to just forget and move on.

Also important to note that you must acknowledge that this loss was purely psychological. Coaches will keep telling you that no such thing exists and will quote Marshall "The most difficult thing is to win a won game" and refer you games of Karpov where he was pawn up and converted without giving the opponent a hint of counterplay. Of course, technique is so very important, but come on, at 2100 level you have that basic technique (which is also clear from your commentary). 

So realize that this is in no way an indication that you're not worthy of your rating. Again - it's just one of those days. Good luck and keep going

Dude I lose 40 points for a defeat like that

And I just lost a 3rd game like that. This time to a stupid 1600. I'm playing terribly HELP

drink water idk

it happens but dont worry you will get them next time, also 2000 is preserved!

Focus on the game. I wish you good luck!

Nope  entering 1900 club

I hit 2500 on chess.com and was on top of the world and just check my account now... I'm back to 2430 and losing game after game (blunder after blunder).

But that's chess.com. You can play as much as you want. OTB is so much more painful