Legal Question in Family Law in Texas

Let son move in and stay with you for 6 months. Then file a motion to modify the parent-child relationship and you will 99% likely win without much of a battle. If your son is willing to talk to the judge, you have SOME chance that you could prevail on a motion to modify right now, without waiting 6 months. However, your son is right on the edge of the age where judges actually care what his opinion is. Once you've had actual possession for 6 months, it's very hard to lose the lawsuit.

Child support to dad will stop as soon as you win the lawsuit.

If you just informally let your son move in and quit paying child support, you will face contempt of court, but, with a good attorney, you can get out of it (probably) by asking the court for credit for the time your son actually lived with you. The problem is that dad will probably force the son to move back if you quit paying.

Going to court either now (good) or after your son has been with you for 6 months (best) is the only way to end child support for you.