For some couples, living apart serves as a trial divorce, a moment for each person to evaluate whether ending the relationship portends greater happiness or at least less unhappiness than continuing it. For others, a separation is a step toward divorce. A legal separation, supervised by a court, can be an end in and of itself for those whose convictions, religion or entangled finances do not permit them to terminate the marriage. If you are heading into a separation, you and your spouse need to negotiate an agreement about core issues, such as marital assets, debts, financial support and child custody.

Separation means different things to different couples. Occupying separate bedrooms can be a type of parting, but generally, the term indicates that a couple is living apart. A “legal separation” is offered in some states to couples who want to separate permanently but cannot divorce, either because of their personal beliefs like religion or complications such as shared health insurance. You may regard your separation as temporary, but once you start living separately, there are no guarantees that you will get back together in the near future.

That’s why the “separation letter” you are contemplating must be a more formal and complete document than you may think. If you are just saying, “I am moving out,” you don’t need any help composing the note. If you want to establish some of the basic financial and personal terms of the separation, you need to work those out with your spouse and/or attorney.

To prepare a document as to how the separation is going to work, you need to invest some time, perhaps a lot of time, depending on how long you’ve been together, in determining what you have acquired in terms of assets and debts and if you’ve have children. Essentially, you need to think through all of the issues that can arise in a divorce and work out resolutions to them.

If you are thinking, “Whoa, this is just temporary for a few months until we make a decision,” ask yourself a few simple questions. Who is going to stay in the house; who is moving out? Who is going to pay the mortgage, the credit cards, the family utilities, the school tuition for the kids? Where will they live? Who will take them to their practices and games?

The truth is that even if you think your separation is short and simple, you need to think about how your life is going to unroll. And not just think about it: Agree with your spouse and get the details in writing. Because this can be used to establish court-ordered divorce (or legal separation) terms, you may want to run the entire matter by an attorney before you sign off.

At the very least, your separation agreement should include: who stays in the house, who takes care of the kids, visitation times for the other parent and financial matters. Keep in mind that if you live in a community property state, you’ll want to think about whether you intend the separation to change your property ownership. In general, all income earned by either spouse, and all property purchased with the income, belongs equally to both spouses. Unless you specify differently, this rule may prevail during your period of living aparAt the very least, your separation agreement should include: who stays in the house, who takes care of the kids, visitation times for the other parent, and financial matters. Keep in mind that, if you live in a community property state, you'll want to think about whether you intend the separation to change your property ownership. In general, all income earned by either spouse, and all property purchased with the income, belongs equally to both spouses. Unless you specify differently, this rule may prevail during your period of living apart.