Sorry to hear what you're going through. It sounds like it is imperative that you speak with a family law attorney ASAP. I suggest using avvo to find a couple close to you and giving them a call - most should offer a free consultation and be able to answer your questions. Good luck.
DWI's are not grounds for the award of sole custody. Commission of crimes is a factor that can be considered.
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My answers are intended only as general legal advice and are not intended to create an attorney-client relationship. There is no substitute for a full consultation with a local experienced criminal defense attorney. For more answers based on my 19 years of experience visit my website, www.austincriminaldefenseattorney.com
Agreeing with Mr. Nielsen, I think it's imperative that you talk to a family law attorney. I would gather as much information as you can on your ex and the police calls to your ex's parents' home.