Put yourself on a "No-buy." Don't allow yourself to buy anything for a set amount of time! (Or at least try to. )
Read the No-buy thread and some people have good advice!
Hope this helped!!
Answered[ Edited ]
To stop spending money on makeup several things work for me. First I go through everything I have and pull out the great colours/products for the season and set them up where I can see and use daily. Next I think about things I need to get that are not makeup or things I want to save for and purchase them as rewards after a specified time of successful not-spending. Also I think about things I'd like to do and spend me time on so that I have a plan and don't find myself bored casually buying things for the sake of buying/collecting. To succeed you need to know where you are starting and have a plan to succeed. Keeping myself occupied and out of stores is usually the best way for an out-of-control habit.
I think I am a poor role model for curbing makeup acquisition! Probably true for most of us here. If I want to cut down my spending and I am going to the store, I take out some money from the bank and when it's gone, I have to go home. But I usually leave the store and lust after stuff I saw there and pretty soon I end up ordering them online.
I recently read that the way to develop willpower is to clench your muscles when you feel your resolve ebbing. I tried it with dessert and it somewhat works for that, but not so much for makeup. But look at it this way, your passion could be for something a lot less innocuous than makeup.
You're not alone, makeuppiggy! A lot of us have trouble with spending too much on makeup and there is a great thread on here about "Shopping Your Own Stash" which is helpful in keeping from purchasing new items.
Here's a link to that thread: http://community.sephora.com/t5/Beauty-Confessions
Also, the thread about "No Buy" is along the same subject line and you can read it here: http://community.sephora.com/t5/Beauty-Confessions
Hope this helps!
Have a great day!