Totally get this sentiment, I’ve found myself here a few times in both Pokemon and other collectibles.
There’s a few different pieces of this that could be delved into a bit, but ultimately I think if you recognize you are buying things just to “get the high” in a sense, want to stop but can’t or don’t know how, and then shortly afterwards move on to find the next thing to buy, you may be in a cycle of what you termed collecting addiction. It’s a tough thing to meter out, no doubt, and as far as I’m concerned it’s analogous to folks who find themselves in the vicious cycle of buying lotto tickets and digging themselves in a deeper and deeper financial hole.
The good news is the overwhelming majority of cards are not 1 of 1 (or even 1 of 100 or 1 of 1000 for that matter), so I think FOMO is (unfortunately) this incessant and annoying devil we choose to keep perched on our shoulder, when in reality, unless you are trying to purchase an item that is quite rare, chances are high you’re not going to actually miss out. That said, “spending more than you should” is really going to be determined by you; spending $100 a month on pieces of Pokemon cardboard for someone who is broke might be crazy expensive, while others can afford to drop thousands of dollars a month if they wanted and their financial situation isn’t really damaged.
I have found in my own life what helps me tremendously with Pokemon spending and enjoyment/hobby spending in general is writing this stuff out so I have some sort of budgeted plan. Even if you don’t stick to it as well as you’d like, it’s very useful to help quantify where you’re headed in reality rather than where you think or hope you may be going. Additionally, it gives you some standard (that you get to define based on your life situation) to actually know what is being deviated from, otherwise all these thoughts/questions/FOMO/“I’m an addicted financial disaster child” end up like a Tangela spaghetti noodle mess in your head. Then, if you go a few months and realize “wow, this really is a problem”, you can recalibrate your plan again to something more fitting, and continue to repeat that process until you have a refined plan as you continue to collect. The kicker is starting that process IMO; it’s always harder to create a good habit, but once you have it locked in it feeds off itself.
The other piece of advice I have gotten from more seasoned collectors is simply taking a step back and revisiting the things you have already acquired (this is why binder collections or wall displays, for example, can be so useful). It’s incredibly easy to get sucked into finding the next thing, but it’s really cool to view some of your favorite items periodically and just enjoy them. This may sound ultra nerdy but even keeping a log of when you bought certain items may be a fun thing to look back at 5/10/15/20 years down the line to see how much ground has been covered!
Tangentially related, there is a thread talking about collecting fatigue linked here, which may be useful to read. While not the exact same question, I feel like they’re both branches that grow off the same tree.
Hopefully some of this is useful. Best of luck! 