Welcome! I have a few things I want you to do:
Unsubscribe from any triggering subreddits and don't visit them. When you want to visit them, go clean a few of your brushes/sponges. Repeat as necessary.
Unsubscribe from any emails that are from companies that send you sweet promotional deals every 8 hours. When you stop seeing new things, you'll stop fixating on buying them.
Go and remove your bank account information from any online makeup store. Make it difficult for yourself to shop there.
If you watch youtube makeup videos, unsubscribe. The only videos you're allowed to watch now are those that are showcasing products you already have.
When you want to buy something go swatch every color you have in the same color family. I shit you not, I have a black eyeshadow in nearly every palette. That's probably 10 different black shadows. Then do it for other common colors you have that you like. Of if lipsticks are your poison, do it with them.
Take care of your pretties. Clean and sanitize the ones that can be cleaned and sanitized. Go through and toss any expired mascara/liquid liner/gloss. Rearrange how you keep everything in a way that reminds you of how much beautiful stuff you already have. If you have the money to spend, or the creativity to do it, get organizers in place so you can see what you have. Love it and appreciate it. You spent a good amount of money on them, don't forget that they exist. I think of mine as having personalities (they don't obviously, I'm not insane) and that way I stop to think of how "sad" they will be to be replaced. Or how "upset" they are that I don't use them as much as I should.
These are the tips that helped me overcome the desire to run out and shop shop shop shop. I was doing it because I was bored. Then I did it because it was just what I did. Then I did it because it felt wrong not to.
Good luck to you /u/makeupandmacaroni. Good luck.