You and your spouse have been arguing a lot, and you finally decide to move out. You live apart for a year. You have your own apartment, you buy your own car and you have to purchase a lot of other things for yourself. You're still married, but you have to operate on your own.
When you finally get divorced, is the property you bought going to count as marital property? Or is it separate property? This makes a big difference when dividing assets.
Generally speaking, it depends on what type of separation you had. You can go through a legal separation, which is very similar to a divorce but which does not terminate the relationship. You still get to make decisions about child custody, property division and other things that would normally be part of the divorce. If it's a legal separation, then you already divided your marital assets and new ones can likely belong to you alone.
However, many couples split up unofficially, in something that is known as a trial separation. From a legal standpoint, nothing changed. You're still a couple, even though you live in two different locations. That means that all of your assets, no matter who bought them, may still count as marital assets. You'll have to divide them.
Of course, there are ways around this. For instance, you could use a postnuptial agreement to protect yourself. But you need to be wary about staying married and living on your own, as it can make that eventual divorce much more complicated. Make sure you are well aware of your legal rights.