HOW DO I BECOME LEGALLY SEPARATED IN TEXAS?
The brief answer: you don't.
Texas does not have legal separation as some other states do. During your separation, you and your spouse are under the same legal requirements as any other married couple. This includes the presumptions of community property and the duty to support each other.
If you want a separation, you basically have two options: contract and temporary orders.
You can enter into a separation agreement, similar to a prenuptial agreement. The same general rules apply to both separation agreements and prenups - in writing, signed by both parties, entered into without coercion, and fair and equitable. The separation agreement allows you to agree upon property issues, support, and child custody and visitation. The agreement is a contract, but the Family Code gives it a special status that makes it enforceable later in a family court.
The other option is to file for divorce and schedule a temporary orders hearing. Temporary orders are basically the rules that govern the litigation. You can't be divorced upon filing in Texas as we have a 60 day waiting period. If you don't establish some ground rules during temporary orders for property, support, custody and decision-making, all the normal rules for a married couple apply. That can be disastrous. The larger counties usually have standard orders that apply to every filed divorce, but most do not. Temporary orders help avoid lapsed house payments, fights over visitation and emptied bank accounts. Get temporary orders.
But do not take temporary orders lightly. Frankly, calling temporary orders "temporary" has got to be the most misleading legalese ever. In the vast majority of cases, temporary orders become final orders. This is especially true in child-related issues. Courts prefer the status quo for children, assuming it is healthy for the kids. If the children have been living at mom's during temporary orders, for example, odds are they'll be living with mom after final orders. The same momentum, though not as binding, seems to apply to property and support issues.
So try to get what you want out of your temporary orders hearing. It's hard because they pop up so fast, but get an attorney quickly and expect that most of your cost will be front-loaded to prepare for that hearing. It's a big deal.
Whatever you do, don't leave it to chance. Ask an attorney to help you to use either contract or court to protect yourself.