How’s this for a Dear John letter. Shortly after Natalia Lusinski broke up with her boyfriend of more than two years, she received a letter from him. It wasn’t a tear-filled note about how much he missed her or even an angry tirade about all the things she did wrong. It was an invoice.

Her ex (who she calls “Kevin” in her story) sent her a bill for $1,797.65 that “included everything from ‘your half of the New York hotel room’ — for a wedding he invited me to — to a $5 pack of cough drops,” she wrote on Business Insider.

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She said that she realized immediately the invoice was a sign of his resentment of how they handled finances as a couple. And although it contributed to a breakup in their case, this is exactly the kind of thing that sends many couples to a therapist.

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“One of the biggest reasons couples come to me is because of finances,” says relationship psychologist Dr. Natasha Sharma. “The stress of finances can be overwhelming.”

In Lusinski’s case, she thought she had squared away the financial rules with Kevin early on. But clearly, they weren’t on the same page.

“A few dates in, he invited me to dinner and asked me to split the bill,” she wrote. “I told him splitting the check was too businesslike and said I’d prefer if the invitee pays — a principle my grandmother instilled in me early on. I also told him I preferred handling money in a way where the person who makes more pays a higher percentage of joint costs.”

While she was under the impression that Kevin was in agreement — he earned more and therefore would pay for things like expensive dinners, while she would pay for less expensive outings — he started to do things like have her pay for an impromptu pack of gum when they went grocery shopping or her share of the bill at his friend’s birthday dinner.

“Looking back, I can’t help but wonder what Kevin and I could have done differently to avoid… money tension in our relationship.”

Sharma says it starts with having an open discussion about money.

“In 2018, talking about money and expectations around who pays for what has to be at the top of your communication list. Don’t let that sit in the back of your head,” she says. “If you’re going to cohabitate, you should know exactly how much your partner makes and vice versa.”

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Furthermore, it’s important to check any money insecurities at the door. While she says many men still feel societal pressure to earn more and may be shy or embarrassed to share this information with their partner, it’s crucial for making the relationship work.

“Whether it means seeing a financial planner or a therapist, you have to get over your insecurities and have an open, honest discussion.”

Even today, many people find the “who will pay on the first date” question to be something of a stumbling block, but Sharma says this can be answered by following one simple rule: the person who invites the other person out should pick up the tab.

But beyond that, it shouldn’t be assumed that one person always does the paying.

“The worst thing you can do is have a set of expectations that you haven’t discussed with your partner,” Sharma says. “Unfortunately, a lot of women still think the man should pay for everything and that’s an outdated mindset.”

She says that may have made sense when men were the providers and women didn’t work, but today that attitude is an indication that other antiquated ideas could permeate the relationship and become troublesome.

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“In this day and age, it’s very shortsighted to think that a relationship can continue in that vein,” she says. “If you have a partner who is financially able and willing to pay for everything, that’s fine regardless of what society says. But what I see most often today is the member of the couple who makes more money contributes more to the joint expenses. That’s fair and manageable.”

Both Lusinski and Kevin demonstrated bitterness and resentment, in Sharma’s opinion, and resorted to petty tactics — all of which could have been avoided.

“It’s a conversation that we talk about more in society, whether it’s in the media or in cocktail conversation, but sadly, too few couples actually sit down and talk about finances.”