I've been playing chess for 10 years and I'm still terrible.

I've been playing chess since I was a kid ~10 years. I've read a number of books and studied openings. I was ~decent, and I peaked at 1500 chess.com. I then stopped playing for a year.cI came back, reread most of the books, and registered a new chess.com account and lichess account. I don't play much on chess.com, but I was 1200 on lichess when I restarted. I then progressively got worse, until I was just 900. (600 or so on chess.com, I would think). I've studied more openings, but I just can't seem to get out.

Does anyone have any tips?

All youre playing is speed chess.   What were you expecting?

Uhhh I only play 10 minute

Like i said...all youre playing is speed chess.  So how are you expecting to improve when all youre doing is moving fast?

Yeah, that’s fair.

I’m rated 1500 Classical on Lichess and 900 Rapid.

I’m honestly just annoyed because I feel like the amount of tactics I’ve studied isn’t congruent with my actual performance.

Unless you're using a different account you should try playing every day. That's what helps me the most

dont play speed...

play bullet that'll help !!

You don't have the time to look for tactics (and neither develop as a player) in speed chess.

Playing with the NaNo ViRuS will severely impede your thinking.

Youre doing the right thing studying tactics.  But it is going to be next to impossible to implement into your games what you are trying to learn playing nothing but speed chess.  Youre not giving yourslf time to think.

Are you analysing your games afterwards ?

It’s important to see where you are making mistakes and work out how they happened.

otherwise you just keep on repeating them ad nauseum.

If you’re rated that low, then you’re probably blundering pieces and hanging mates all over the place. So any type of study: whether it be tactics, openings, whatever, will show you very little ‘return on investment’. You have to go back to the absolute basics and work on board vision, safety, and so on. 

Thanks

I often lose, get upset, and walk into my next game without a clear head and I end up getting a disadvantaged position and just resign. 

i really want to know what books you are reading. You dont need any of that at your level to improve.

Have you tried preserving ojas. The more I preserve the better I play

I'm just not sure how to not make these kinds of blunders. 
I methodically go through a 'checklist' in my mind for most moves I make, and I look at all my opponent's pieces to see how it is attacking my own. Then, I look at how my opponent's piece could attack my own. Then, how I can attack my opponent's pieces. If I find something, then I look at the potential drawbacks. (Can I be forked, pinned, mated). If I don't find anything then I try to apply tactics. (How can I control files, how can I develop my pieces, am I blocking any of my pieces.) Whenever I blunder I think I just completely miss what my opponent can do when going through my checklist.

Improving Your Chess - Resources for Beginners and Beyond...

https://www.chess.com/blog/RussBell/improving-your-chess-resources-for-beginners-and-beyond

I think 10 mins is decent for me, not even considered speed chess. You should probably go to longer games though. Not too much longer, I'd say 15 minute games would be easier. Remember that the brain gets slower with age. Also don't waste your time studying openings, they're definitely not the problem. You should practice on the puzzle rushes, I find them extremely helpful. I always do at least 2 before a game, it's nice to warm up.

instead of openings you should practice on the lessons. You only need one or two openings and basic knowledge of them. Memorization isn't too helpful in chess, it's a game of adaptation.

Off the top of my head, I've read a chess endgames for beginners book. "Logical Chess: Move By Move", a book about openings, and then a book about how to respond to 1. d4.