I am terrible with money. I like to spend it whether I have it or not. This is not acceptable to my boyfriend, who has to make our pennies stretch as far as possible. Other than just "trying harder," what can I do so that I don't over-spend?

Good question.
Were it me, I would start by taking whatever I make and depositing it into a bank account (direct deposit from work is great for this). Then I would make a list of everything that you NEED to get by in a month. By "need" I mean things like food, water bill, vibrator batteries...you know: necessities. Finally, I would set aside the money I need and keep the rest inside the bank account.
NOTE: Destroy your credit cards!
Don't think about it just do it!

The single best thing you can do is set yourself a budget. This is basically where you look at what you earn each month, you subtract your fixed expenses (these are things like your rent and electricity bills and taxes) and see what you have left to play with. You then divide this up, assigning a realistic amount to each expenditure you have left (food, clothes, eating out, home entertainment, cosmetics.. whateve ryou spend on - for some things you will probably have to budget nothing at all.) Include things like holidays and presents that aren't spent every month - work out what you would likely spend in a year on this and divide by twelve for the amount you need to put aside for this. Obviously don't go over the amount you earn, and try and have around 10% of your earnings unallocated for savings or debt repayments as appropriate (this can also be used for a genuine emergency - such as if you flood your flat and your insurance won't cover it.)
You then write up this budget and stick to it come hell or high water. If you budget £12 for cinema visits, and you spend £12 in the first week - that's just no more cinema visits for the rest of the month.

I find it helps if my money goes into an account on pay day, and I have direct debits for all my bills, rent etc going out of this account ON PAY DAY - so I don't get chance to spend the money earmarked for bills. I also have a regular transfer from this account set up into one or two other accounts which I use for my food shopping and my entertainment/clothes etc budget - this helps me to keep track of my spending.

Also - try to find ways to get the things you buy cheaper. This can turn into a fun challenge in itself - I actually enjoy seeking out where I can buy my favorite make-up for the lowest price, rather than just walking into the first high street shop I pass and paying full whack. Buy generic brands of things where possible to keep costs low. Use the internet to compare prices - look out for special offers and discount vouchers - they really help.
Also, if there's a luxury you really can't afford but feel you can't live without - try and find a way you can rais ethe money to pay for it - by selling something you no longer use on ebay for example, or taking on a second part time job, or doing paid market research. That way you needn't feel guilty as it has been paid with "extra" money, not your standard income.

First step. Cut all your credit cards. Then yes make a budget.

The strategy you have to develop will require you determining how you spend your money. Is it clothing? Try shopping at outlets or things like Marshall's. If you're already shopping there, thrift stores can be fun and funky. Are you spending your money on eating out? Learn to cook. Drinking at bars? Start a hobby where you can hang out with your friends at home.

That is where a lot of my money leaked. I started playing poker at a friends house every Tuesday. It's a $12 buy in and I bring my own alcohol. It's fun, and if I lose it's not very much. If I win, I get money back!

you are trying to comfort yourself with "stuff"-otherwise you wouldnt be so disrespectful of your boyfriends hard work. it will take therapy, and years to figure out what you are comforting yourself about, and why money is so unimportant to you. in the mean time, you need a plan. the next time the "I WANT IT MONSTER" emerges you will do what instead of indulging?

Develop a budget and stick to it.