Although you cannot finalize a divorce until your baby is born, you can most certainly begin the process by filing the petition for divorce! Keep in mind that Texas is a community property state, so the assets (property and income) belong to both of you. Find a local family law attorney ASAP, and get the divorce started. Unless he can prove you a danger to the children, the fact that the child will be newborn will make it more likely that your husbands visits will be short, but frequent. If you can show the Court that he is not stable, they may be supervised. Don't waste time getting the evidence together, and contact an attorney immediately! Good luck!
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I agree with the other attorneys. I would like to add that if he is medically discharged, he may be eligible to receive disability benefits based on his mental health conditions. A portion of these benefits may be awarded to you as child support. If his mental stability is a major concern, I recommend that you start keeping a journal or timeline of your observations of why he may be unfit to be a parent. Keep in mind that mental health records are generally privileged in Texas civil courts, but can be disclosed in limited circumstances.