Overspending isn't caused by the VISA card. The VISA card is simply the mechanism through which you are overspending. Credit cards are neither good nor bad -- they are simply a tool.
Having said that, I have heard that the average person spends as much as 30% more -- thinking of a situation like the grocery store, Target, a restaurant; that is, places where it's easy to feel that it's okay to splurge just a little, to order a soda instead of water, to pick up a $6 magazine or an expensive steak -- when they're spending with plastic instead of cash. Think about that and decide whether you're prone to that particular issue or not. You said you find it "sooooo easy" to spend plastic -- you may be one of those people. A person to whom spending on credit doesn't feel like real spending.
The real issue is to control your spending, and towards that end I'll give you several ideas:
- If you think cash only will help you, try it for one month . . . and then decide whether it was a good choice. Personally, I don't see much point in that -- not when the real issue is to learn to spend more wisely -- but we all have this or that little trick that works for us.
- Don't just spend -- work out a budget for yourself. Allow some wiggle-room for things upon which you know you'll spend, and make "saving" a big line item in the budget. Then no matter what form of currency you're using, stick to that budget. Based upon what you're saying, I suspect that impulse buying is one of your issues, and a budget will help you learn to control it.
- Start recording your spending. For some people -- and I suspect you're one of them -- buying with plastic doesn't "feel real", so they don't tend to "mentally count" what they've charged, and then suddenly a BIG BILL arrives in the mail. We started our oldest daughter with a small credit card ($300 limit) when she was a senior in high school; we encouraged her to use the card, but we had her attach a post-it note to the back of the card and every time she used it, she recorded how much she'd spent. Then when the bill came, she'd pay it and stick on a fresh post-it. She's now a college junior and is managing her very limited funds well.
As for credit scores, don't focus on them. Your goal should be financial stability, which is NOT the same thing as a good credit score. A person with financial stability is living within his means, is either out of debt or is working towards that goal, and is increasing his net worth each month. In contrast, a person with a good credit score can be up to his eyeballs in debt, living paycheck-to-paycheck, but is paying at least the minimum each month. It's critical that you understand the difference between these two situations.
Finally, pointing out the obvious: Using your fiancé's VISA card will not build up YOUR credit score, though it may help hers.