Legal Question in Family Law in Texas

If your son is at least 12, you can file a motion to modify the existing order, with the basic reason given that living with you is what's in your son's best interests and is what he has indicated he wants to do, and ask the judge to talk to your son about it. Assuming that conversation goes well (he doesn't say he wants to live with you because you let him eat candy for breakfast and skip school, whereas dad makes him do his homework and clean up his room), the judge will probably change custody to accommodate your son's wishes, unless there's some good reason not to that you haven't shared here.

If your son is under 12, it doesn't work quite the same way. You'd still file the same basic motion, but would instead need to focus on some compelling reason(s) why living with you would be in your son's best interests, and in this scenario, I'd strongly encourage you to try to get outside support for your position from some responsible adult (maybe one of his teachers) who knows your son and the situation well enough to be able to testify if needed as to why you'd be a better choice for custody.