Parsimonious by nature, I spent hours taking each monthly bill, working out exactly how much I paid out each week, dividing that figure by seven, then doubling it to get the precise cost of Joff's stay in terms of food, electricity, gas and so forth. I kept a tally of how much he owed me in a little red book. I'm ashamed to say that it crossed my mind more than once to charge him interest.
It was only after a bout of particularly complex calculations which left Joff's debt approaching pounds 2,000 that I suddenly asked myself what on earth I was doing. How and when exactly did I expect him to pay me back? Then finally it hit me: we were going to stay together and the money didn't matter. What's yours is mine, and mine yours. From then on life was much more straightforward. We merged what little we had into a joint bank account, and nine years on the only money problems we've encountered are the usual ones of not having enough.
Not so for many couples. According to the marriage guidance service Relate, money is one of the three main causes of relationship problems, along with children and sex. Julia Cole, a couples counsellor, thinks it is due in part to the growing gender issue surrounding the way couples handle their money.
"Until quite recently many women stayed at home and the man was the principal earner. Now for the first time we've almost got a situation where men and women are earning equally, which is reflected in the way couples are tussling with money issues. Money says something important about our general understanding of relationships at a time when the whole structure of marriage has changed, and is no longer seen as binding for life."
But Ms Cole also believes that money is often a code for deeper and more complex psychological issues. While separate finances are standard at the beginning of a relationship when people are still assessing what it means to make a commitment, the arrival of a mortgage or children usually heralds a deepening sense of security and confidence.
"Those who remain fixed on keeping things absolutely separate are often revealing something about the whole nature of their relationship," she says. "They may be a committed couple, but have a deep need to remain independent, or they may be fearful the relationship won't last."
Carol, 38, has kept a strict fiscal his 'n' hers with her partner, Mike, for 15 years. "I would never, ever trust anyone with a shared bank account," she says. "It's just asking for trouble. Supposing Mike were hypnotised by some 18-year-old floozy and cleaned me out? I'm a worst-case-scenario person: I plan for the worst possible outcome. Love just doesn't come into it where money is concerned."
The benefits many of us see in pooling our resources are lost on Carol. "It's merging something that ought to be kept quite separate. It's part of our respect for each other's privacy - I wouldn't dream of looking at Mike's bank statements, for instance. It's also about personal freedom: what's left after you've paid the bills is entirely your own, to spend on yourself. I've just spent pounds 35 an hour on some therapy sessions, and I can do that without feeling guilty. It's my pure self-indulgence money."
Although Mike, an engineer, earns far more than Carol, who works in publishing, the costs of family life are split right down the middle. Carol gathered three months' worth of food bills and totted them up to get the weekly average, deducted the cost of Mike's beer, then divided the rest "to the last tomato"; every month she pays an pounds 80 standing order into Mike's account for her share of the food.
Similarly, both pay half the mortgage, each recalculating their repayments and amending their standing orders whenever the lending rate changes. Ditto the nanny-share for two-year-old Sam, and most of the other household bills. The only exception is the Council Tax, which Carol pays in full. "When the bill came addressed to the head of the household, I was determined that should be me," she says.
It is a system that works for them, and one Carol rigorously adheres to. Despite paying bank charges on her overdraft for the past six months, she wouldn't dream of asking Mike for help. "Why should he?" she asks.
Nor does she feel resentful that Mike has much more to spend on himself. "He does have more surplus, but I think if you start going on about fairness you're into big political principles. It's your choice how much to earn; I don't really care, because I'm comfortable.
"Mike earning more than me is not the source of conflict so much as the issue of my labour. I put far more into the house and looking after Sam, as well as having a full-time job, and I fail to see why I should wait hand and foot on him for nothing." Carol recently decided to get a cleaner; Mike is paying.
However, since Sam's birth, Carol does admit they've let things slip a little. "The household costs have blurred a bit more since he was born. I suppose I am becoming less uptight about it. We are a family now, and I can see it's going to take something fairly major to split us up."
While some would see Carol's concerns about money as a lack of confidence in her relationship, others would argue that she shows genuine realism. Brian Capon, from the British Banking Association, spent 10 years as a bank manager. He warns that although joint accounts are the most common way to deal with family finances, they are not the most secure.
"Many people don't realise that the danger of a joint account is that if one party goes out and spends a lot of money, or deliberately runs up a great deal of debt, the other is liable. If your partner runs off abroad, you are responsible for any debts. It's worth bearing in mind the `what if' when you set up a joint account; the vast majority do go perfectly smoothly, but you have to think about whether you are really comfortable that you can be left in that position."
Mr Capon's advice is based on sound principles, but many people would regard such concerns as too clinical. When it comes down to it, they argue, marriage is a partnership built on trust, and that is reflected as much in finances as in fidelity. For instance, when 33-year-old Josey Maciel met her husband Michael, a freelance IT consultant, 11 years ago, he showed absolute confidence and trust in her from the outset.
"I was a student at the time and from the moment we started living together we had joint bank accounts," says Josey. "Michael looked after me financially, even giving me a credit card. He didn't put any limit on what I spent. I used to take my friends out for meals on his money, and buy myself clothes. And even though I had no money he bought the house in joint names and paid all the mortgage."
Josey went on to pay her way for many years before giving up her job to have Aliya, now four, and Yakira, 10 months. In the meantime she set up a vegetarian food production company. "At the moment I'm still trying to get the business off the ground, so Michael is putting pounds 1,000 a month of his earnings into it. He's been doing that for the last three years."
Michael, 37, is perfectly reconciled to their past and present financial arrangements. "After all, when I was just starting up my business, Josey was the only one putting a salary into the account," he says. "It's just very convenient this way. We never argue about money, although Josey tends to spend a lot more than me.
"When it comes down to it, Josey is someone I love and can trust, and the way we deal with money shows the total commitment between us. Why would we do it any other way? We're a couple, a partnership, not single people"n