Am I stupid ?

Why did you play 7. d4? Your bishop is under attack after his Na5. Your bishop was being protected by the pawn you pushed which could easily be taken by your opponent's pawn.
Seems to me that this started your house of cards collapsing.
It is possible that you just might not have any real aptitude for Chess to get to be very good. Nevertheless, just like many golfers who have never broken 100 or tennis players who can only beat players who are very unatheltic, keep playing. Regardless of all this, join a local club and or get an instructor to help point out your errors and how to prevent them. On this site, play correspondence Chess and join Vote Chess to see how good players reason out how to make good moves. This should be a good start.

When I started playing I probably played 10 games a day every day and won maybe 4 games a week. Did this for over a month.
Eventually you get past the anger and frustration, at least it passes faster.
yes it does time pasts faster with anger and frustration - its just the anger and frustration take its toll on ones mind faster too-- then pleasantness and winning which you can savor making time past too quickly

Apparently my personality is the exact opposite of yours. You are an optimist and I am a pessimist.

Your rating is 800, you aren't expected to win a against 2000 rated coach.
I've seen 800ELO guys on this forum saying they beat 2000 cpu. So I thought I could do it too.

unpleasant existence...
That's right. Defeat is nothing but an unpleasant existence.

bro you are an 800. Even I can't beat David. (not that im good or anything but) Don't get frustrated, solve puzzles, and most importantly, PLAY REAL PEOPLE. Don't play the bots too often.

Your rating is 800, you aren't expected to win a against 2000 rated coach.
I've seen 800ELO guys on this forum saying they beat 2000 cpu. So I thought I could do it too.
I think what a lot of them do is just play the same bot like 50 times until they win and then they go brag in the forums, saying "I beat David!!" without telling people that they lost 49 times before that.
I'm sure you can beat David, but it might take a lot of attempts.
Why do you guys never give up on chess no matter how many times you lose?
For me, losing is a great humiliation, a shame, and an extremely unpleasant existence.
It always infuriates me.