Blunders ruin my games

You're probably reading the title and thinking "obviously", right? I just can't find a way to stop it from happening. I always try to think about checks, threats, and captures. I've been watching YouTube videos, been going to a local club and playing, studying openings, but I just can't improve because I'll eventually drop a piece. It takes an absurd amount of thinking power for me to not blunder and I just can't get better.

Here's a game I played today as an example. I'll hold a steady lead the entire time, making good moves for me, and then BAM I blunder a mate in two...

I feel like I have a good understanding of higher level play too, but until I stop hanging pieces it just won't manifest itself in my rating  Anybody else struggle with this or have advice?

If you are playing chess with a decent time control and you have selected your move, study the board to see if the other side has a one move killer.
Or before making your move apply the undefended test which at move 30, was a4, c4, e4 and f1
Do this *every* move ( Or being realistic with the game above move 9. ).

Back in the day when I was a reasonable player I had a list of pre-move things to do.
Write one yourself that suits you.
Then find a few games of say 1500 ELO players and go through their game with your list compared to their moves. (enough of them appear on this site for comments).

In the game above prior to white's 10. BxB I was already looking at a2, c3 and b7
I did not favour your 10. Ba3  (10. a4 for me) but saw immediately it was applying pressure to the new undefended d6 while the b7 issue was on going.

Obviously 30. Ra6 was a really, really bad move, but I only imagine you were very impatient with your next move. It may've been a sense of stress, but what I like to do is, whenever my opponent plays a move, think "Huh, why did he play that move?" Sometimes it's a simple answer. "Oh, he wanted to develop his bishop!" or "Oh, she's attacking my knight!" If I was in your position, I would think "Oh, he's attacking my Rook and looking to Mate in 2 me!" and proceed to play 30. Qg2.

Are you very stressed? It will affect your focus. Maybe a glass of wine or a bath before playing online would help.

Whenever you are seated in front of the  computer screen or at the  chessboard table in over the board play sit on your hands.

It will cause that  extra moments hesitation in reaching for the mouse or reaching  for the piece or pawn.  That extra moment will keep you from blundering.

Do You notice You got Yourself in a hot water positionally before blundering? Disconnecting rooks by Bc1, then exchanging thaqt bishop at the moment it has became a chief defender of dark squares, softening Your kingside position just before the lines opened? Positional blunders prepared a tactical blunder. I'd go 21.Nc3 followed by Nd5, then Bd2, and only then doing anything on queenside.

Unfortunately for you, your opponents often reward moves like 30.Ra6 with losing their knight next move, which reinforces this kind of analytical behavior.

For example, let me ask you, after 30.Ra6 what move did you expect your opponent to play? You didn't think of that right. You were hoping you'd just win the knight. I assume you didn't even think of a knight move because he can play Nxe4 with a scary attack. This is what I condescendingly call "hoping you get to move twice in a row."

Anyway, yes, it does take a lot of mental energy to do this for the whole game. It IS very hard... at first. Give yourself long enough time controls where you can attempt to do it on every move. Practice and painful losses like this help develop the habit of checking. The more you get used to it, the less energy it takes until it's natural.

It is hard, and it is discouraging, but you can improve.