When two people choose to marry or move in together, they both need to make compromises to maintain harmony inside the house. Those compromises may entail many different things, but finances are definitely something to keep in mind and one really important issue to discuss beforehand. Couples choose to approach budgeting in different ways, but the most important part is that both are in agreement and stick to what they've decided for the sake of their wallets and of the relationship.
The issues begin when one of those parties actively chooses to go over budget, provoking problems and/or showing that they don't care about their joint financial stability. It's even more problematic when they already have big fixed expenses, like paying rent or a mortgage.
This couple went through an issue of this kind. They both split all their expenses 50/50, including utilities and mortgage. They both cover half of the mortgage every month, but this time, the husband was making some extra big expenses without talking about it with his wife. He bought a gaming console, a set of new golf clubs, and went away for a weekend with his buddies. He spent so much that he ran out of money to pay for his part of the mortgage and asked his wife to cover it. In other words, he expected her to pay for the entire mortgage by herself that month. Naturally, she refused. He was supposed to take care of half of the payments and be responsible for his own finances. He didn't, and now he feels annoyed because his wife doesn't want to take responsibility for his missteps. He claims that they're 'supposed to be a team'. Well, if they are a team, each of the members has to take care of their own responsibilities for the entire system to work smoothly.
No matter whether you have joint finances or individual finances. One is always responsible for their own money and can't demand that others take care or our own mess-ups and reckless behavior.